What is the world's largest fighter plane?

The prototype YF-12A version of the SR-71 was about 114 ft. long, which is much bigger than the F-14. Technically the largest fighter plane in history (an aircraft designed to engage another airborne object) was the Boeing YAL-1, a heavily modified 747 armed with a massive high powered laser intended to shoot down incoming ballistic missiles (no, I'm not kidding). Only one was ever built and the project was cancelled in 2014.