The Mitsubishi A7M2 Reppū (Strong Gale, Allied reporting name "Sam") was a naval fighter plane developed as a successor to the infamous Type Zero carrier-based fighter.
The result of the 17-shi carrier-based fighter specifcation, the Zero's sucessor (then referred to as Navy Experimental Type 17 Type A) was expected to be able to climb to 6,000m in less than 6 minutes and then fly above that altitude at 639km/h, all while carrying two 20mm cannons and two 13mm machine guns and retaining the A6M3 Zero Model 32's impressive manueverability.
Engine selection was a primary problem - meeting the specifications required a 2,000hp powerplant, of which all available options - the Nakajima NK9 and the more powerful Mitsubishi MK9 - were still in development. With a larger engine capable of the required output, wing-loading became an issue - the Navy had requested no more than 150kg/m², which the MK9 was expected to fulfill. Due to MK9 production delays however, the Navy instructed Mitsubishi's design team to use the Nakajima NK9.
The Specification 17 carrier fighter's development was further delayed due to production facilities prioritizing production of the A6M-series fighters and Mitsubishi's G4M bomber as well as fixing issues with A6M variants and Mitsubishi's J2M Raiden. The A7M1 Reppū prototype finally flew in May 1944, demonstrating excellent handling and manueverability but could not attain its lofty 640km/h target due to the underpowered NK9 engine. The Navy ordered development stopped due to the failure, but Mitsubishi obtained permission to test the aircraft with the MK9 engine.