Defense Acquisition Research Journal Leading Change The Defense Acquisition Review Journal (ARJ) is a scholarly peer-reviewed journal published by the Defense Acquisition University (DAU). All submissions receive a blind review to ensure impartial evaluation. Articles represent the views of the authors and do not necessarily reflect the opinion of the DAU or the Department of Defense. October 2024 Vol. 31 No. 2 | Issue 107 Journal DOI: 10.22594/dau.042023-103.30.02 Elect ISSN: 2156-8405
ARTICLE LIST
The Next Great Engine War Was Not What You Thought It Was Col James Rodriguez, USAF
One Small Step for Space Acquisition Doctrine Maj Roman Tillman, USSF
The “Shrinking” Defense Industrial Base: A Survey of Former DoD Prime Contractors Edward Hyatt and Lloyd E. Everhart
BOOK REVIEWS
The Kill Chain: Defending America in the Future of High-Tech Warfare Written by Christian Brose Reviewed by Christopher McGowan The Touchstones of Leadership: Essential Principles for Business Leaders Written by Joseph Carleone Reviewed by Chris D’Ascenzo DBA, Professor of Program Management, DAU
We’re on the Web at: http://www.dau.edu/library/arj
Michael P. Duffey Under Secretary of Defense for Acquisition and Sustainment Bilyana Anderson President, DAU
Angela Carsten Chief of Staff, DAU Christen Goulding Director, DAU Communications and Public Affairs
Editorial Board Dr. Larrie D. Ferreiro Chairman and Executive Editor
Dr. Michelle Bailey Catholic University of America Dr. Don Birchler CNA Dr. John M. Colombi Air Force Institute of Technology Dr. Cynthia R. Cook Center for Strategic and International Studies Dr. Bobbie G. DeLeon DAU Dr. William T. Eliason Eisenhower School for National Security and Resource Strategy Dr. J. Scott Frampton Eisenhower School for National Security and Resource Strategy Dr. Steve King MITRE
Jeffrey R. LaFleur Eisenhower School for National Security and Resource Strategy David H. Lewis Naval Postgraduate School William Lucyshyn University of Maryland Dr. Thomas A. Mazzuchi The George Washington University Dr. John Mccormack University of Manchester (UK) Dr. John G. McGinn
Dr. Troy J. Mueller MITRE Dr. Christopher G. Pernin RAND Dr. Yvette Rodriguez DAU Dr. Dana Stewart DAU Dr. David M. Tate Institute for Defense Analyses Dr. Trevor Taylor Royal United Services Institute (UK) Dr. Marina Theodotou Office of the Secretary of Defense Jerry Vandewiele DAU
George Mason University Dr. Georgella McRae DAU Patrick Morrow DAU Dr. Robert F. Mortlock Naval Postgraduate School
ISSN 2156-8391 (print) and ISSN 2156-8405 (online) DOI: https://doi.org/10.22594/dau.072025-109.32.02
The Defense Acquisition Research Journal , formerly the Defense Acquisition Review Journal , is published quarterly by the DAU Press and is an official publication of the Department of Defense. Postage is paid at the U.S. Postal facility, Fort Belvoir, VA, and at additional U.S. Postal facilities. Postmaster, send address changes to: Editor, Defense Acquisition Research Journal , DAU Press, 9820 Belvoir Road, Fort Belvoir, VA 22060-5565. The journal-level DOI is: https://doi.org/10.22594/dauARJ.issn.2156-8391. Some photos appearing in this publication may be digitally enhanced. Photos in this publication may have been sourced from the Department of Defense website (https://www.defense.gov/Multimedia/Photos/). The appearance of the U.S. Department of Defense visual information does not imply or constitute Department of Defense endorsement. Some images may be digitally enhanced. The views expressed in the Defense Acquisition Research Journal are those of the author(s) alone and not of the Department of Defense. Reproduction or reposting of articles from the Defense Acquisition Research Journal should credit the author(s) and the journal.
Chief of Visual Arts & Press Norene L. Johnson Interim Managing Editor Dr. Olena McLaughlin Assistant Editor Christopher McGowan Art Director, DAU Press Michael Krukowski Lead Graphic Designer Paul Kim Production Manager
Frances Battle Graphic Designer, Digital Publications Nina Austin Technical Editor Collie J. Johnson Copy Editor/Circulation Manager Michelle McDonald
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The Next Great Engine War Was Not What You Thought It Was Col James Rodriguez, USAF
The author compares and contrasts the various "engine wars" starting with the F-15's engine competition, fifth-generation engine procurements (F-22 and F-35), and finally, adaptive cycle engine technology development. He emphasizes the value of competition and the need for clear requirements to drive technological investments, leading to recommendations including technology roadmaps to facilitate transition pathways and funding technology maturation programs to ensure healthy competition.
One Small Step for Space Acquisition Doctrine Maj Roman Tillman, USSF This qualitative research study engaged 45 DoD acquisition professionals in a comprehensive survey to uncover best practices that could inform the first-ever acquisition doctrine of the U.S. Space Force. Using the blueprint developed in this study, the Space Force can develop acquisition doctrine not as a point of departure but to lead the Service toward reemphasizing the importance of acquisition as a warfighting spacepower discipline. The “Shrinking” Defense Industrial Base: A Survey of Former DoD Prime Contractors Edward Hyatt and Lloyd E. Everhart This study empirically examines the issue of Defense Industrial Base (DIB) contractor exit with a survey of contractors likely to have exited between Fiscal Years 2015 to 2021 to ascertain if they have left the DIB and, if so, why that was the case. The results offer unique insight into a critical area of concern for the defense acquisition community by identifying the types of contractors that have exited and the specific reasons for doing so, including those reasons that are within DoD’s ability to influence.
From the Chairman and Executive Editor Dr. Larrie D. Ferreiro
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Perspectives and Commentary
Call for Authors We are currently soliciting articles for the 2026 Defense ARJ print year.
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The Next Great Engine War Was Not What You Thought It Was Col James Rodriguez, USAF
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One Small Step for Space Acquisition Doctrine Maj Roman Tillman, USSF
The “Shrinking” Defense Industrial Base: A Survey of Former DoD Prime Contractors Edward Hyatt and Lloyd E. Everhart Professional Reading List The Kill Chain: Defending America in the Future of High-Tech Warfare Written by Christian Brose Reviewed by Christopher McGowan The Touchstones of Leadership: Essential Principles for Business Leaders Written by Joseph Carleone Reviewed by Chris D’Ascenzo, DBA, Professor of Program Management, DAU Current Research Resources in Defense Acquisition A selection of new research curated by the DAU Research Center and the DAU Virtual Research Library
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Defense ARJ Guidelines for Contributors
FROM THE CHAIRMAN AND EXECUTIVE
EDITOR Dr. Larrie D. Ferreiro
The theme for this issue is “Competing for the Next Industrial Base.” In the current Great Power Competition, the United States is focusing on strengthening domestic capabilities, fostering innovation, and ensuring a resilient and competitive industry to meet future national security needs on land, sea, air, and even in space. The first paper is “The Next Great Engine War Was Not What You Thought It Was” by James Rodriguez. In this case history, the
author provides a fresh look at the competition for Air Force fighter engines during the 1980s and 1990s between two industrial giants, Pratt & Whitney and General Electric. The so-called “Great Engine War” yielded better-performing engines at significant cost savings, which was not repeated for the fifth-generation fighters of the 2000s. The author argues that the lessons of successful competition should be applied to the new adaptive engines for future platforms. In the second paper, “One Small Step for Space Acquisition Doctrine,” Roman Tillman attempts to develop the framework for a formal Space Force acquisition doctrine based on existing Space Force tenets, DoD and Air Force acquisition guidance, and other examples of acquisition doctrine. Using several analytic tools including manual assessment and two AI platforms, the author determined the emergent best practices that reinforce the proposed doctrinal blueprint. The author contends
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that these can help the Space Force develop acquisition doctrine as well as re-emphasize the importance of acquisitions as a warfighting spacepower discipline. The third paper is “The ‘Shrinking’ Defense Industrial Base: A Survey of Former DoD Prime Contractors” by Edward Hyatt and Lloyd E. Everhart. As the title implies, in recent years, the defense industrial base has diminished in terms of number of contractors and companies, which in turn may have adverse effects on America’s warfighting capabilities. The authors empirically examined this issue by conducting a survey of contractors who exited the defense industrial base between Fiscal Year (FY) 2015 and FY 2022, to determine why they left. Many of the respondents (generally smaller businesses) cited unfavorable characteristics, including payment difficulties and contracting hurdles, as reasons for departure. These results demonstrate where the DoD can influence acquisition policy and processes to improve the health of its critical supplier base. This issue’s Current Research Resources (courtesy of the DAU Virtual Research Library) focus on “China as a Strategic Opponent in Great Power Competition”. The Defense Acquisition Reading List features the following book reviews: • The Kill Chain: Defending America in the Future of High- tech Warfare by Christian Brose, reviewed by Christopher McGowan. • The Touchstones of Leadership, A Comprehensive Guide for Business Leaders by Joseph Carleone, reviewed by Chris D’Ascenzo. Robert "Bobby" Ralston has left the Editorial Board. We thank him for his devoted service.
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DEFENSE ARJ IS NOW ACCEPTING PERSPECTIVES & COMMENTARY SUBMISSIONS
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Guidelines for Contributors:
Defense ARJ invites long-form articles that provide perspectives and commentary on pressing matters that concern defense acquisition and lay the groundwork for future action and research. These articles should identify topical issues of relevance to the defense acquisition community, sufficiently document the issues and their consequences using appropriate references and citations, and arm the reader with actionable information in the form of recommended solutions and/or potential research questions. They must be rooted in real- world circumstances. Perspectives & Commentary articles should contain the following components: • Introduction • Background • Relevance to the defense acquisition community • Analysis of issue/problem, and outline of consequences under the status quo • Proposed solutions and/or potential research questions • Summary • References For more information, contact the Defense ARJ managing editor (DefenseARJ@dau.edu) and check out our Guidelines for Contributors at https://www.dau.edu/library/darj/ guidelines-contributors
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CALL FOR AUTHORS We are currently accepting articles for the 2026 Defense Acquisition Research Journal (Defense ARJ) print year. We welcome submissions describing original research, case histories, and perspectives and commentary from all acquisition career fields and phases of the acquisition life cycle—the conceptualization, innovation, initiation, design, testing, contracting, production, deployment, logistics support, modification, and disposal of weapons and other systems, supplies, or services (including construction) needed by the DoD or intended for use to support military missions. Articles should ideally be 5,000 words or fewer. The editorial team will consider longer submissions on a case-by-case basis. Articles should never exceed 10,000 words. All manuscript submissions are peer reviewed.
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All submissions should include the following items:
• Cover letter • Manuscript • Figures and tables • Biographical sketch for each author • Headshot for each author Benefits of publishing
• Share your research results with the defense acquisition community. • Change the way DoD does business. • Become a nationally recognized expert in your field or specialty. • Be invited to speak at a conference or seminar. • Earn up to 40 continuous learning points. For more information, contact the Defense ARJ managing editor (DefenseARJ@dau.edu) and check out our Guidelines for Contributors at https://www.dau.edu/library/darj/guidelines- contributors
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We’re on the Web at: http://www.dau.edu/library/arj
ISSUE 109 SUMMER 2025 VOL. 32 NO. 2
The Next Great Engine War Was Not What You Thought It Was
THE NEXT GREAT ENGINE WAR WAS NOT WHAT YOU THOUGHT IT WAS
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Col James Rodriguez, USAF
In the 1980s, the Air Force oversaw a period of engine development that author Robert Drewes coined, “The Great Engine War.” The fierce competition between Pratt & Whitney (P&W) and General Electric (GE) yielded two world-class fighter engines, an energized competitive industrial base, and significant cost savings. When the Air Force competed engines for the Advanced Tactical Fighter, the engine war continued; however, it did not progress beyond the fly-off. After a pause, the Great Engine War appeared ready for restart when Congress pushed for a Joint Strike Fighter (JSF) program dual-source approach. However, the battle between GE and P&W for the JSF engine was short-lived as budget constraints forced the DoD termination of GE’s F136 engine program. Recognizing the need for continued propulsion research and development, the DoD then initiated the next potential Great Engine War, a series of technology development programs to develop a new generation of adaptive engines. As the Air Force seeks to field adaptive engines in future platforms, it must reflect on the lessons of the Great Engine Wars to ensure a healthy, technologically advanced, and agile fighter engine industrial base remains postured to win the coming Great Power Competition.
DOI: https://doi.org/10.22594/dau.24-928.32.02 Keywords: F-35, propulsion, adaptive, competition, acquisition
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Since April 15, 1953, the United States has maintained unmatched air superiority, not allowing a single death of U.S. ground troops by enemy aircraft (GE Aerospace, 2023a). In the following decades, air dominance has been a critical enabler of how the U.S. military fights, maneuvers, and projects combat power worldwide. Although air dominance requires a fusion of multiple technologies, fighter aircraft engines are one of the most challenging and complex mechanical systems ever produced. They require tremendous engineering talent, immense precision, advanced manufacturing techniques, and cutting-edge material science, among other factors. These challenges were not overcome by chance but through a long history of creative acquisition solutions, bitter competition, and revolutionary technology development (Drewes, 1987, pp. 15–16).
The fierce competition between Pratt & Whitney (P&W) and General Electric (GE) yielded two world-class fighter engines, an energized competitive industrial base, and significant cost savings.
In the 1980s, the Air Force oversaw a period of engine development that author Robert Drewes coined, “The Great Engine War.” The fierce competition between Pratt & Whitney (P&W) and General Electric (GE) yielded two world-class fighter engines, an energized competitive industrial base, and significant cost savings (Drewes, 1987, p. 128). When the Air Force competed engines for the Advanced Tactical Fighter (ATF) (predecessor of the F-22), the engine war continued; however, it did not progress beyond the fly-off. After a pause, the Great Engine War appeared ready for restart when Congress pushed for a Joint Strike Fighter (JSF) program dual-source approach. However, the battle between GE and P&W for the JSF engine was short-lived as budget constraints forced the DoD’s termination of GE’s F136 engine program. Recognizing the need for continued propulsion research and development, the DoD then initiated the next potential Great Engine War, a series of technology development programs to develop a new generation of adaptive engines. Once again, the first set of adaptive engine programs met a similar fate as the F136 engine when the Adaptive Engine Transition Program (AETP) was discontinued in the Fiscal Year (FY) 2024 budget before production (Tirpak, 2023). Despite these missed opportunities, the United States still enjoys dominant aircraft propulsion systems
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characterized by world-class thrust, unmatched reliability, and enviable safety records. Still, propulsion competitions have become characterized by generational winner-take-all decisions (Mayes, 1988). In his Accelerate Change or Lose guidance to the Air Force, then U.S. Air Force Chief of Staff Gen C. Q. Brown stated, “Air Dominance is not an American birthright” (Air Force Chief of Staff, 2020). The DoD must replicate the lessons of the First Great Engine War to ensure we maintain propulsion dominance. The next Great Engine War has stagnated because the DoD needs to build a requirements and cost-informed propulsion roadmap that drives technology investment and promotes competition. Furthermore, although the AETP failed to transition to the F-35, the program successfully maintained a competitive industrial base through an extended development phase, ready for renewed competition for sixth-generation and beyond applications. The DoD does not need to field systems with dual-source engines as long as it designs technology development pathways like AETP and follows up with a transition to programs of record to maintain a healthy two-vendor propulsion industrial base. Great Engine War Background Despite unmatched air superiority since the 1950s, the Vietnam War served as a stark reminder that technology must continue to evolve to stay ahead of the adversary. After experiencing loss rates of one aircraft per 12 enemy aircraft in Korea, the United States lost one aircraft for every 2.5 enemy aircraft shot down in Vietnam (Drewes, 1987, p. 10). To counter emerging Soviet threats, the Air Force initiated the F-X program, which eventually evolved to become the F-15. Furthermore, despite Service disagreements, DoD leadership forced the Air Force and Navy to start a joint engine development program since the engine requirements for the Navy’s F-14 program were similar enough to the F-15 to utilize a common engine (pp. 12–14). The Air Force was chosen as the lead Service. Desiring to take advantage of numerous advancements in propulsion technology, the Air Force sent Requests for Proposal (RFPs) to GE, P&W, and the Allison Division of General Motors, seeking to double the thrust-to-weight ratio of currently available engines (Camm, 1993). In February 1970, after hardware testing, the Air Force selected P&W’s F100 engine, although GE’s offering was compelling. Drewes (1987) identified the reasons for such selection in historical documents on F-15 engine development:
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… it was felt GE had a better engine structurally and control-wise but a higher risk fan in the stability area. The P&W aircraft engine was assessed to be considerably heavier and lacking a real control system but had a fan/ compressor with more potential to meet specifications. P&W also demonstrated a greater understanding of engine/inlet compatibility phenomena. (p. 31)
Over the next few years, technical challenges and component testing delays began to mount. Furthermore, delays in the Navy’s F-14B program significantly increased, eventually causing the cancellation of the procurement of Navy engines. According to Drewes, the Navy’s cancellation forced the Air Force to renegotiate a now sole-source contract with P&W, yielding a $522 million cost increase. Seeking to reconstitute a larger engine buy after the Navy pulled out of the F100 program, the Air Force also selected a variation of the F100 for its F-16 fighter. Shortly after fielding, in 1974, the F100 engine began to experience two serious issues: stall stagnation that required the pilot to shut down and restart the engine in flight and an extremely short life that drove up operations and sustainment costs. As detailed in a RAND study led by Frank Camm, the conditions for the Great Engine War were set. Since the Air Force had granted numerous schedule and testing concessions during development, the Air Force wanted P&W to fix these problems. However, P&W argued that they had met the engine specifications and
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had warned the Air Force of the high operating costs. P&W stood ready to resolve the issues as long as the Air Force compensated them fully for the work. These contractual issues led Air Force officials to become dissatisfied with P&W’s attitude, and they believed that P&W would be more responsive and willing to fix the problems if viable competition existed (Camm, 1993). Having been effectively shut out of the fighter engine market, GE started looking for ways back in. With the F-14 having canceled P&W’s engine procurement, GE built a demonstrator engine with components from its F101 and F404 engines. Still, due to the likely costs, the Navy did not have interest in re-engining the F-14 despite congressional additions specifically addressing the problems. However, since the proposed GE engine design inherently solved the F100’s stall stagnation and operating costs challenges, and with growing frustration with P&W, the Air Force wanted to support further GE engine development (Camm, 1993). The initial funding turned out to be an easy sell, as the Air Force convinced Congress to appropriate $82.5 million, which was then supplemented by a reprogramming of an additional $33 million from $41 million that had been provided to begin development of an alternate engine for the F-14 (Ogg, 1987).
Shortly after fielding, in 1974, the F100 engine began to experience two serious issues: stall stagnation that required the pilot to shut down and restart the engine in flight and an extremely short life that drove up operations and sustainment costs. As detailed in a RAND study led by Frank Camm, the conditions for the Great Engine War were set.
With the industrial base clearly in mind, the Air Force justified GE engine development in congressional testimony, stating, “P&W will be working from a development funding base … in excess of $2 billion and an experience base … of 14 years. GE will be working from a development funding base … of $0.7 billion with no previous experience” (Camm, 1993; Drewes, 1987, p. 101). At the time, no one thought that GE’s engine would actually compete against P&W for future requirements; the primary intent was to use the threat of competition to promote
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better responsiveness and performance by P&W and to have a standby, demonstrated technology. Fast-forward a few years, in 1981, the Air Force was ready to initiate a real competition to replace the F100 and issued a Request for Information to the companies asking what the Air Force could expect from a competitive proposal.
P&W and GE continued developing their engines to include higher thrust models that could meet emerging requirements and were eager to compete. In 1983, the Air Force issued an RFP stating that consideration would be given to the effects of “dual awards,” offering the first clue that the Air Force was considering a split purchase. However, in public messaging, the Air Force emphasized it had no preconceived plan to split the requirement. The RFP solicited contractors to submit proposals for an estimated 2,000 engines and offer prices for multiple procurement profiles, including single-year and multiyear options for possible Navy procurements. After months of evaluation, in February 1984, the Air Force announced a split award of a single year’s engines: 120 GE engines for F-16s and 40 P&W engines for F-15s. Because of the pricing matrix in the contractors' proposals, the source selection authority chose to award only a single year and allow the contractors' performance and field experience to influence future year procurements. Surprisingly, P&W nearly lost all of the engines in that first year, as their proposal included a step function in the pricing matrix so that costs increased significantly if anything less than a 100% buy occurred. Believing that continuing to foster competition for the engines was necessary, the Air Force gave P&W a share of the initial award despite the increased price (Drewes, 1987, pp. 117–118, 126–127).
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Though controversial, the Government Accountability Office (GAO) concluded that the Air Force’s decision to split the procurement was reasonable despite the increased costs of a dual award, and that the competition and source selection procedures were fair (GAO, 1984). Additionally, GAO concluded that the Air Force’s recognition of other perceived benefits, such as the potential for additional future savings, increased contractor responsiveness, an enlarged industrial base, and protection from production disruptions, were reasonable factors to consider. Over the next few years, competition drove each company to compete for a larger share of the annual quantity by offering lower prices and improving customer relations. The strategy appeared to work, with procurement quantities shifting over the next few years back to P&W's favor, as detailed in Table 1 (Mayes, 1988). TABLE 1. ENGINE PROCUREMENT QUANTITIES AND PERCENT BY FISCAL YEAR Fiscal Year GE (Quantity / Percent) P&W (Quantity / Percent) FY85 120 / 75% 40 / 25% FY86 184 / 54% 159 / 46% FY87 205 / 56% 160 / 44% FY88 147 / 45% 181 / 55% FY89 100 / 39% 159 / 61% FY90 39 / 36% 70 / 64% Total 795 / 51% 769 / 49% The primary outcome of the Great Engine War was GE’s success in reentering the large fighter engine market by unseating the incumbent, an infrequent occurrence in DoD procurement practice. When the Air Force announced its decision to split future purchases in February 1984, P&W had delivered over 3,000 engines valued at over $10 billion (Ogg, 1987, p. 15). Today, GE and P&W are still competing as the F-15 and F-16 Foreign Military Sales (FMS) markets remain strong, and the U.S. Air Force is acquiring the new F-15EX powered by GE’s F110. Despite P&W's head start, the Great Engine War ended in a near 50/50 split, as GE has produced 3,400 F110 engines, while P&W has produced more than 3,800 F100 engines (GE, 2019; Mayes, 1988; P&W, n.d.). It is challenging to ascertain whether competition yielded the $3 billion savings the Air Force estimated over 20 years. However, a case can be made that competition ensured the United States had two viable engine suppliers that produced world-class engines with unmatched reliability and safety.
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Discussion With the F100/F110 engine war in full force, the Air Force started developing its next fighter, the ATF. Looking to capitalize on the newly infused energy in the propulsion industrial base, the Air Force issued contracts to GE and P&W in 1983 for ATF engine development through ground tests. In bidding for the ATF’s engine demonstrator contract, GE and P&W were free to use whatever technical approach they felt best to achieve the performance goals. P&W had taken a technologically aggressive approach with its F100 engine, which, though they won the contract, earned them years of headaches in maturing that technology to the Air Force’s satisfaction. For the ATF, P&W instead emphasized “somewhat lower risk technology and high reliability” (Younossi et al., 2002). On the other hand, GE was burned by P&W’s higher performing engine, which cost the company 10 years of fighter engine contracts when it lost to the F100. It finally sold its F110 engine by “stressing the reliability and simplicity of its … engines” when the rival F100 suffered enough problems to force the Air Force to look at alternatives (Aronstein et al., 1998). To avoid a repeat of the ATF, GE adopted P&W’s previous high-risk approach by demonstrating high performance and advanced technology from the outset, leaving problem solving for later. Instead of a traditional turbofan engine like the F110, GE chose to push its higher performance but technologically unproven variable cycle engine.
P&W had taken a technologically aggressive approach with its F100 engine, which, though they won the contract, earned them years of headaches in maturing that technology to the Air Force’s satisfaction.
The results of the flight tests reflected the different approaches. GE’s push to meet higher thrust requirements resulted in its YF120 engine significantly outperforming the YF119 in the YF-22 and YF-23 . It showed better high-mach performance and was preferred by the airframe companies for their high angle-of-attack flight tests. Nevertheless, in August 1991, the Air Force announced that P&W’s YF119 won the ATF engine contract. Though GE’s performance was outstanding, the Air Force was reportedly concerned about the risk involved with the YF120’s
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variable cycle design. P&W also had a reputedly better management plan and development schedule “that was considered extremely responsive to customer needs” (Aronstein et al., 1998). P&W had won the first battle for a fifth-generation aircraft engine, and the decision proved final, with no subsequent engine war to revive the YF120 engine for the F-22.
In the spring of 1995, airframe contractors Boeing, Lockheed Martin, and McDonnell Douglas all began competing during the concept development and risk reduction phase of the DoD’s JSF program, designed to create affordable aircraft for the Air Force, Navy, and Marine Corps. Given the relative maturity of the F119 and its design heritage as a fifth-generation compatible engine, all three contractors elected to incorporate a derivative of the F119 as the engine for their conceptual designs. Concerned about the growing P&W dominance of military fighter engines, Congress directed the Joint Program Office (JPO) to pursue a second engine source to maintain competition; therefore, in late 1995, development contracts were awarded to P&W for an F119 derivative that eventually became the F135, and to GE for an F120 derivative that would subsequently become the F136. Congress intended to follow the model of the Great Engine War, with JSFs eventually fielded with both F135s and F136s. DoD continued funding both engine developments until 2007 when the department proposed termination of the F136 since the development of the F135 was
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progressing well, and that anticipated savings from competition would not offset the upfront development cost (Younossi et al., 2002). Congress rejected the termination, restored funding, and kept the program funded in 2008, 2009, and 2010 despite continued termination in the DoD budget requests. Finally, in 2011, Congress agreed to terminate, and funding ceased (Gertler, 2012). Although the program was eventually canceled, many officials expressed concern that the termination was driven more by near-term budget pressures than the long-term potential benefits. On the other hand, some officials applauded the decision, stating that single-source production contracts are the best strategy for long-term affordability. Congressional testimony was also mixed, with Secretary of Defense Donald Rumsfeld testifying that the merits were “clearly debatable” and Secretary of the Air Force Michael Wynne testifying that he was worried about the “downstream effects” of the decision. Regardless, the DoD and Air Force continually argued that despite the concerns of senior leaders, the F136 did not make sense from a pure “business case,” hinting that other factors, such as industrial base capacity and resilience, weighed on the decision (Murch & Bolkcom, 2008). Numerous studies were commissioned to argue the merits of the alternate engine, including one by the Office of the Secretary of Defense Cost Analysis Improvement Group (OSD CAIG), which noted that although skeptical of the financial benefits, nonmonetary benefits could be gained. The most notable potential benefit concerned the need for growth potential in the JSF engine. The OSD CAIG report predicted that the engine would eventually need to be upgraded for additional thrust. Since the F135 was already close to exceeding design temperature specifications, it would require further modifications beyond the F136
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to allow for thrust growth (Murch & Bolkcom, 2008). The OSD CAIG’s prediction turns out surprisingly accurate during the future F135 and Adaptive Engine Transition Program decisions, which will be described later. Independent reports from the GAO and Institute for Defense Analyses similarly concluded that a financial break-even point was uncertain; there were numerous nonfinancial benefits, including fleet readiness, contractor responsiveness, industrial base resilience, and more robust international relations (Murch & Bolkcom, 2008). Despite these potential benefits, Congress relented, and the F136 program was canceled. From 1994 to 2009, P&W received $7.3 billion for F135 work, while the GE/Rolls Royce (RR) team received $2.4 billion for F136 work (Gertler, 2012). The Adaptive Engine War (GE’s XA100 vs. P&W’s XA101) In 2007, the DoD chose to eliminate funding for the F136 in the President’s Budget request and instead initiated the Adaptive Versatile Engine Technology (ADVENT) program through the Air Force Research Laboratory (AFRL). The program was intended to support technology development from initial design to a full-engine demonstrator. Unfortunately, the funding provided would require a down-select after design and allow for only one contractor to proceed from design to building the demonstrator. The program office described the vision for the new program as “multi-point design engines that automatically adjust fan & core airflow and pressure for optimized performance & fuel efficiency at all flight conditions.” In other words, unlike previous engines optimized at a single design condition (typically cruise), these “variable cycle” engines could adapt airflows to provide maximum efficiency across various flight conditions, significantly decreasing fuel consumption. A stated program goal was to reduce fuel consumption by up to 25% (Hunter, 2021, p. 57). An important concept to enable these fuel efficiencies is the introduction of variable bypass. An engine’s bypass ratio refers to the amount of air flowing through an engine fan compared with the portion going through the combustor. Higher bypass ratios are generally found on engines designed for long-distance cruise, such as transport or passenger aircraft. Lower bypass ratios are generally found on fighters that require more thrust. A variable bypass is designed to change the bypass ratio from low
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for high-speed performance to high for cruise, by using a third stream of air separate from the combustor and traditional bypass flows. Depending on flight conditions, the third stream can be increased or decreased to adjust the bypass ratio. In 2007, after a short initial contract requiring P&W, GE, and RR to explore conceptual designs for notional aircraft applications, the Air Force awarded a $296 million contract to RR and a $231 million contract to GE to proceed into the design and ultimately demonstration (Flight Global, 2007). Although not explicit, the contract served as a concessionary prize to partially make up for the termination of the F136. Since the Air Force did not have sufficient funding to fully fund both contracts, the contracts contained a clause stating that the Air Force would provide authorization to proceed into the demonstration portion of the contract based on technical viability and available funding. P&W’s bid was unsuccessful, meaning the company would have to devote internal research and development funds to continue adaptive engine work or risk losing the dominance it enjoyed with the F135. As the GE and RR design teams progressed, the program continued to gain visibility and prominence. With the DoD desiring both companies to achieve technical parity, additional funds were reallocated to ensure that both contractors could test a demonstrator engine. Still, AFRL required each team to test the engine's core. The core consists of the high- pressure compressor, combustor, and turbine. GE successfully tested its core in late 2012, achieving records for the highest pressure ratios and temperatures the Air Force has ever tested (Jordan, 2014). Meanwhile, in 2012, plans for a follow-on program, Adaptive Engine Technology Development (AETD), were being conceived. Politics played a prominent role in the follow-on, with the F136 battle recently concluding with
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cancellation. Connecticut senators challenged the Air Force, saying that the AETD program was the first step toward developing a new engine for the F-35 . The Air Force was adamant that the program was purely technology development. In August 2012, when the Air Force awarded follow-on AETD contracts to GE and P&W, congressional objections to AETD were dropped (Warwick, 2012). The Air Force award to GE was unsurprising as GE had performed strongly in ADVENT. However, P&W’s award was a huge payoff on the gamble they had placed in self- funding their own rig tests while execution of the ADVENT program had been ongoing without them. AFRL considered AETD the bridge that transitioned adaptive engine technology from the laboratory over the proverbial “valley of death” to the Warfighter in 2020 (Norris, 2015). The Air Force needed to apply real-world constraints to the ADVENT proof of concept to increase the likelihood of transition. Lacking a specific aircraft platform, the Air Force chose the only fighter currently in production, the F-35 Lightning, as the air vehicle to apply constraints such as size, weight, and location of aircraft bulkheads. Despite constraining the engine to the F-35 Lightning, the Service recognized that the adaptive engines could be applicable to future sixth-generation fighters, the next long-range bomber, tanker or cargo aircraft, or other legacy aircraft (anonymous personal communication, 2024, January 11). During the execution of AETD, the AFRL began partnering with the Air Force Life Cycle Management Center’s Propulsion Directorate to hand the next follow-on, the Adaptive Engine Transition Program (AETP), to the center responsible for fielding systems. In 2014, the Propulsion Directorate’s program office received direction from Office of the Secretary of Defense (Acquisition, Technology and Logistics) to competitively award a contract by September 2015 to complete technology maturation and risk reduction efforts and support future engineering, manufacturing, and development (EMD) decisions. Unfortunately, despite this direction, funding was not phased appropriately across the Future Years Defense Program to enable program initiation in 2015. The DoD published a Resource Management Decision in January 2015, removed the previous start constraint, and rephased funding. However, the delay resulted in significant slips to acquisition planning milestones and contract awards. In June 2015, the Air Force Service Acquisition Executive Dr. William LaPlante approved the AETP Acquisition Strategy, which included awarding two noncompetitive contracts with the new funding in place.
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In June 2016, the AETP program office awarded two separate $1.01 billion contracts with a period of performance through September 2021 to GE and P&W (Ripple, 2016). The program's goals were to complete the design, manufacture, and ground test of two full-scale, flight-weight, F-35-sized prototype engines. Additionally, the engines were expected to increase the F-35’s range by at least 25%, increase thrust by 10%, double the power management, and improve thermal management compared to the incumbent F135 engine (Hoehn & Parrish, 2022). One of the major design considerations the Air Force chose to implement was intentional incompatibility with the F-35 Short Take-off and Vertical Landing (STOVL) variant. Aircraft engines must be sized to meet an aircraft’s most stressful operational conditions. For the F-35, the STOVL variant drove the F135 design, therefore compromising performance for the F-35A and C variants, a phenomenon referred to in the engine community as the “STOVL compromise” (anonymous personal communication, January 11, 2024). As the program progressed through design, contractual options were awarded to further focus on specific aircraft configurations. Option I was exercised to allow for additional integration and testing for an F-35A design, and Option II was exercised to initiate risk-reduction efforts for future air superiority applications. Over the next few years, the program remained a high-visibility program, with numerous briefings and updates requested by senior Air Force and DoD leadership. However, the program remained without a clear transition path to a platform, a fact of which Congress soon took notice. In the Senate Appropriations Committee–Defense Markup
of the FY 2020 Appropriations Bill, the committee noted that the DoD planned to conclude the AETP program in FY 2021 with ground testing; and that no programs, including the F-35, are signaling a demand for the next-generation engine, or budgeting appropriate resources to transition. The committee expressed frustration that failure to transition into production would constitute a “severely missed
opportunity to capitalize on more than $4 billion” and “open the door to our adversaries to eclipse fielded U.S. engine technology in the coming years” (Department of Defense FY 2020 Appropriations Bill, 2019).
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Furthermore, the report directed the Secretary of the Air Force to provide a roadmap to transition in the FY 2021 budget submission, including cost, schedule, competition, and transition plans to other programs supporting advanced engine development, EMD, and production activities. The Air Force, apprehensive about committing to technology that was not fully proven, remained noncommittal, stating that transition plans would be informed by the results of the ground testing (anonymous personal communication, January 11, 2024). While the Air Force wrestled with the following steps, the program continued executing, initiating testing of GE’s XA100 engine in December 2020 (GE Aerospace, 2021). Over the next three years, the XA100 completed three phases of testing, logging hundreds of hours of whole-engine performance and operability testing, including time at the Arnold Engineering Development Complex, where the engine was “flown” at simulated altitude pressures and temperatures (GE Aerospace, 2023b). The Air Force initiated testing of P&W’s XA101 in late 2021 (Tirpak, 2021). Few details on the XA101 testing are available in the public forum. However, the Congressional Research Service reports that the engine was still in testing as of September 2022 and that the XA101 testing remains on track and aligned with the Air Force’s development timeline (Hoehn & Parrish, 2022). Meanwhile, separate from AETP, the F-35 powerplant, the F135 engine, had started experiencing challenges. As detailed by the GAO, F135 sustainment posed the most significant sustainment risk for the F-35 over the next 10 years. F-35 aircraft needing engine repairs were growing, with 20 aircraft down for engine maintenance by the end of 2020. The JPO was projecting that if nothing was done, the program would have
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a deficit of 800 operational engines by 2030 (GAO, 2022). According to the GAO, two primary factors impacted sustainment costs. The first was unscheduled maintenance on the power module, which was significantly higher than anticipated due to a flaw in the turbine coating. Second, the engine depot at Oklahoma City Air Logistics Complex had insufficient capacity to repair modules, resulting in a large backlog. Furthermore, engine life was being decreased due to increased aircraft cooling requirements being placed on the engine. The F-35 uses its power and thermal management system (PTMS) to cool aircraft systems that generate heat, such as the avionics system. The PTMS is driven by bleed air pressure from the engine. While the engine had been designed to meet the air pressure requirements, subsequent upgrades to aircraft systems continued to increase the bleed air requirements (GAO, 2023a). When those upgrades were formalized in 2013, it was too late to redesign the engine without significant cost and schedule impacts. Therefore, program officials accepted the increased wear and tear on the engine. According to the GAO, the current Block 4 modernization efforts will require even more cooling capacity and bleed air than the PTMS, and engine can support and will exacerbate the engine life issues. The GAO estimates these cooling challenges have added $38 billion to the F-35’s life-cycle cost estimate. In response to these challenges, program officials have determined that it must upgrade the PTMS and engine to reduce life-cycle costs (GAO, 2023b).
Given the challenges of the F135, Congress doubled down on the Air Force’s continued lack of AETP transition planning and pushed the DoD to field AETP to the F-35A. Section 242 of the FY 2022 National Defense Authorization Act (NDAA) required DoD to develop an acquisition strategy for transitioning the engine to the Air Force’s
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F-35A version (NDAA, 2021). While the Air Force started preparing an acquisition strategy, in late 2021, the F-35 JPO initiated a propulsion modernization business case analysis (BCA) to evaluate five engine and four PTMS options to meet emerging Warfighter requirements for restored engine life, increased power and thermal capacity, range, acceleration, and increased vertical lift for the F-35B STOVL variant (anonymous personal communication, January 11, 2024). Upon completion, the results of the BCA were briefed to numerous stakeholders, including the JSF Executive Steering Board and the Deputy Secretary of Defense’s Management Action Group (anonymous personal communication, January 24, 2024). Ultimately, Secretary of the Air Force Frank Kendall announced the difficult choice to forgo fielding AETP to the F-35, citing the $6.7 billion cost and incompatibility with all variants of the F-35 as the primary causes (Tirpak, 2023). Instead, the DoD chose to continue upgrading P&W’s F135 engine through the Engine Core Upgrade program. Although the DoD decision appears to be final, congressional direction for AETP is unclear. The 2024 NDAA recommended $588 million to continue technology maturation and risk- reduction activities to buy down risk for the Next Generation Adaptive Propulsion (NGAP) program, planned for integration into the Next Generation Air Dominance (NGAD) aircraft (NDAA, 2023a). Furthermore, The NDAA also required the JPO to establish requirements for the propulsion, PTMS, and electrical systems that adequately support all planned mission system upgrades (NDAA, 2023b). Although this language does not explicitly favor AETP, testimony provided to the House Armed Services Committee by the GAO expressed concern that the F-35’s BCA lacked key details, including requirements that were not fully defined, costs that were not fully assessed, and technical risks not fully considered (GAO, 2023a). In March 2024, an FY 2024 Appropriations Act was signed into law, including $280 million to “develop advanced engine technologies for integration into future engine development programs”; this funding is separate from NGAP funding (Further Consolidated Appropriations Act, 2024). The bill supported the DoD's decision to forgo integration on F 35, even prohibiting the use of the funds for activities to integrate into F-35. However, it remains uncertain how the Air Force will use this funding to continue AETP, although, at least for now, activities are funded to continue.
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Since the BCA results were not made public, and the decisions were made at the most senior levels of the DoD, interviews of multiple senior DoD officials involved in the decision-making process or directly involved in the programs were conducted by the author. Many of the officials still serve in the same roles; therefore, identities will be anonymous for this article to ensure transparent responses. A few themes emerged when asked what the primary factors were in the decision not to field AETP to the F-35. Nearly all interviews revealed that the dominant factors were cost and tri-variant commonality. From a cost perspective, the development/integration costs of $6.7 billion were considered manageable; however, the procurement costs weighed heavily in the decision. Although the AETP engine costs were eventually projected to be only slightly more expensive than an F135, the F135 had the benefit of being 1,000+ engines down the learning curve (anonymous personal communication, January 17, 2024). This phenomenon, paired with the question of what to do with the in-service F135 engines, drove DoD to estimate AETP cost between $20 billion-$38 billion (depending on whether fuel savings were included) when compared to upgrading the F135 (anonymous personal communication, February 7, 2024). Tri-variant commonality was the second primary factor that weighed in the decision. All U.S. and international users of the F-35 maintain a configuration that maximizes commonality across all three variants, including the F135 engine. The F135 engine comes in two variants: a conventional take-off and landing (CTOL) version for the F-35A and F-35C, and a STOVL-compatible version, which includes a drive shaft to power the lift-fan, bleed-air ports to feed the roll posts, and a vectoring nozzle, though both versions share significant part numbers. Incorporation of AETP into the fleet threatened further division of conventional configurations, stranding the STOVL engine and diluting the benefits of international partnership and the global sustainment strategy (anonymous personal communication, January 17, 2024). Although cost and tri-variant commonality were the primary factors weighed in the decision, senior DoD decision-makers also considered the value of the operational benefits of increased range, thrust, power, and thermal capacity, and the value of re-inserting the threat of competition back into the F-35 engine program.
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