I'm retired USAF. Had troops and friends that came from the SR-71 program. (Dan Diamond and Mike Kerbs)
The Nailheads were "procured" for guys that worked in the AGE (Aerospace Ground Equipment) shop and created/maintained the AG-330 start carts.
Paired 401 Nailheads with a Dyanaflo transmission and a "coupled drive" shaft from the cart that interfaced with a starter receptacle on each of the J-58 engines of the SR-71. The carts engaged each J-58, and ran to provide RPM until "TEB" (Triethylborane) was introduced in the combustor section to "light off" the engines, and then as the engines reached their critical (self sustained) RPM, and the start cart was disengaged.
In a few instances, the Nailheads encountered "overspeed" condition, but it was considered a better outcome to overspeed the cart, than have the J-58 stagnate and incur damage, and a few Nailheads "gave up the ghost".
As time went on in the program, the nailheads were replaced with 454 Chevy engines, but they were soon replaced with a Pneumatic Air Start System (because the Chevy solution could not hack the program....)
"When Better Technologies Are Built - Buick Will Build Them..."
Everyone else, is second place, and no one ever remembers second place....
