Much has changed about the Pentagon’s Joint Strike Fighter program in the past 13 years, but one thing has remained steady: the number of F-35s to be bought for the Air Force, Navy and Marines.

All three variants have seen design tweaks, program managers have come and gone, and the projected price tag has climbed and climbed. Meanwhile, the world changed as well, while wars in Afghanistan and Iraq sucked money from long-term weapons projects. Through it all, Pentagon officials maintained they would need exactly 2,443 combat F-35s, plus 14 development aircraft, to deter and fight potential adversaries such as China.

But now radical extremists are wreaking havoc across much of the Middle East and northern Africa, and Russia has re-emerged as a major foe. On Thursday morning, Gen. Joseph Dunford, the Marine Corps commandant nominated to become the next chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee that the F-35 buying plan is under review.

“Given the evolving defense strategy and the latest Defense Planning Guidance, we are presently taking the newest strategic foundation and analyzing whether 2,443 aircraft is the correct number,” Dunford wrote in response to questions asked by the committee in advance of his hearing Thursday. “Until the analysis is complete, we need to pursue the current scheduled quantity buy to preclude creating an overall near-term tactical fighter shortfall.”

Dunford’s comments come one week after Army Gen. Martin Dempsey, the outgoing JCS chairman, warned in a new National Military Strategy that the military might need to rethink and reorganize for the hybrid wars of the future.

That doesn’t mean the F-35 — the largest weapons program ever, by many billions of dollars — is going away. “With projected adversarial threats challenging our current capabilities in coming years, the Joint Strike Fighter is a vital component of our effort to ensure the Joint Force maintains dominance in the air,” Dunford wrote.