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.

Though never built, the XF-108 left a legacy in later aircraft and missile systems, influencing everything from the A-5 Vigilante to the AIM-54 Phoenix. It remains one of history’s most ...