Rarely seen and rarely photographed, one of NA's ultra secret design ideas of WW2. They weren't sure whether to call it the P-262 or V-51. But it was designed to counter the Luftwaffe's attempt to send their own large 4 engine bombers across the pond to bomb America. No really! it's true!

Actually in an attempt to prolong the live of the "Mustang" as a front-line fighter a pair of Ford PJ-31-1 pulsejets were fitted on to the under side of the wings. The results were similar to the Soviet experiments on piston engined aircraft with added pulsejets, an increase in top speed when in use, but with excessive fuel consumption and high drag when not, the idea was dropped soon after the tests.
A couple other ideas

