Designed to hit Mach 3 and destroy Soviet bombers, the XF-108 Rapier could have been one of America’s fastest jets — but it ...

But given the XF-108’s gross weight of 76,000 pounds, the high-thrust engines were necessary. Offering a 0.77 thrust-to-weight ratio, the XF-108 was expected to climb at 45,000 feet per minute.