Gee, Bell never had a 390mph prototype, regardless of whether or not it had guns.
The XP-39B first flew on Nov 25th 1939 and belly landed on Jan 6th 1940, repaired and flown some more it crashes after 28 total hours.
The First YP-38 flies in Sept 13th 1940, also unarmed and around 3 month after the French and British order. One day after first flight of YP-38 the US orders 623 AIrcobras with wing guns and leak proof tanks.
Armed YP-38 makes 368mph? with 1090hp.
View attachment 488449
at 6592 lbs. Please note plane in picture has no guns
who thought an extra 60hp was going to add over 20mph to the plane? especially with extra weight and extra equipment?
WHy did Bell build that one-off special and devote all that time to the drag reduction measures and special paint?
ANd it's the British fault the production machines could come close to the contract speed?