the P-75 could have been classified as "a group of parts flying in formation."
In April of 1942, the famous designer Donovan Berlin of the Curtiss P-36 and P-40 was assigned the task of meeting the requirements for the new fighter. To keep down costs and shorten development time, he decided to use existing aircraft sub-assemblies already in production.
It was made up from sub-assemblies of other airplanes that were already in production. It used the tail of the Douglas SBD Dauntless, the wings of Curtiss P-40 Warhawk and the landing gear of the Vought F4U Corsair.
While it may be fun to poke at GM for the failure of the P-75, they have to be commended for the monumental effort in converting their eastern automotive division to aircraft production. This involved a complete tear down of its five eastern automotive assembly lines and its parts division, and completely rebuilding these facilities practically overnight.
The program was cancelled after only a small number of prototypes and production aircraft had been completed, as it was no longer required in its original role, could not be quickly deployed, and possessed no significant advantages over aircraft already in production.
or read a far better written, and thorough description here: https://www.militaryfactory.com/aircraft/detail.asp?aircraft_id=420