Mitsubishi A7M Reppu "SAM"

The Mitsubishi A7M Reppū ("Sam") was never used in active combat or mass-produced during World War II. It was a prototype-stage carrier-based fighter developed for the Imperial Japanese Navy to succeed the A6M Zero, but only around 10 prototypes were built before the war ended. 
 
Key Details Regarding Usage:
Active Service: Zero; the aircraft never entered active combat duty.
Development Status: Only a small number of prototypes (roughly 2 A7M1 and 7-8 A7M2 variants) were completed.
Operational Context: Development was plagued by engine delays, an earthquake in December 1944, and Allied bombing raids, which halted production.
Final Disposition: Prototypes were tested in Japan, and some were found in hangars (e.g., Yokosuka) at the end of the war. 
 
Designed as a high-performance interceptor to counter Allied aircraft like the F6F Hellcat, the A7M's intended role was for defense, but it arrived too late to be deployed.