Pentagon officials are saying results for the F-35B Joint Strike Fighter tests aboard the USS Wasp fell short of expectations.

Initially, the Marine Corps reported the aircraft performed so well, they declared it combat ready -- an assessment the Pentagon's top weapons tester shut down.

Pentagon Operational Test and Evaluation Office director Michael Gilmore criticized the tests for not being realistic enough.

In a memo obtained by the Project on Government Oversight through a Freedom of Information Act request, Gilmore said a more accurate assessment would have to be under "conditions that were much more representative of real-world operations than those that were used during this deployment."

In the memo, Gilmore also mentions the test's lack of diversity with other aircraft used, and that "key combat mission systems were not installed in the aircraft or were not cleared for use."

In the test referred to by the Marines as Operational Test 1, six F-35s failed to achieve the number of required flight hours necessary to be declared combat-ready.

The F-35 program is the most expensive weapons system ever developed by the Pentagon, amounting to around $400 billion including cost increases and delays in development.

However, other military officials remain enthusiastic about the program's future. Marine Corps Lt. Gen. Jon Davis serves as deputy commandant for aviation, and referred to the project as a "great success."

Gilmore is calling for the Marine Corps to perform an additional, more thorough examination of the aircraft, however, with "a more aggressive set of demonstration objectives."