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Gilmore also seemed to contradict an Air Force announcement that its version of the plane was combat-ready, writing that in its current state, the F-35 would need support from older craft to “locate and avoid modern threats, acquire targets, and engage formations of enemy fighter aircraft due to outstanding performance deficiencies and limited weapons carriage available.”

The current issues with the plane include software problems which continue to surface at a steady rate, and which Gilmore wrote interfere with target identification, communications between aircraft, and radar signal detection. The latter would be particularly significant, since the F-35 is prominently billed for its stealth capabilities.

The current version of the plane’s software, known as “Block 3i,” also leaves the plane’s front-mounted machine gun unusable. Gilmore also wrote that flight testing has fallen “far behind” schedule. Operational testing of the plane is scheduled to begin in 2018.

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Representatives of the military and Lockheed insisted that the memo outlined issues that were already well-understood and were being addressed. Lockheed’s spokesman said that development was still on track for completion in late 2017, while Air Force Secretary Deborah Lee James emphasized that the plane would continue to develop further over “the next several years.”

The F-35 has been the repeated subject of controversy since the inception of the program, particularly over rapidly escalating costs. In 2010, the Senate Appropriations Committee wrote that the program showed “the lack of proper control in the defense budget process.” The plane itself has been described as less maneuverable than older fighters, operating at a disadvantage in a simulated dogfight with the older F-16.