This is the YF-12. If it looks like the SR-71, that’s because it is. The YF-12 was to be a high-speed interceptor - meant to get to attacking bombers faster and engage them before they were over populated areas and could drop their nuclear bombs and do damage.

The YF-12 had a top speed of Mach 3.35, or roughly 3600 km/hr at 80,000 feet. Each plane carried only 3 missiles, and it was an interceptor - meant to go at the enemy, in a straight line.

Could it turn? Well, we frequently consider 9g to be the limit of acceleration for human-piloted jets. Assume, perhaps generously, that the plane can maintain that speed in a turn. 3600 km/hr is 1000 m/s, and a 9g turn would have a radius of over 11.3 km.

But at Mach 4, that turn is 20km in radius. Except that you won’t make that turn at 9g, but maybe 2g because the air is too thin and the wings are too small. That’s a turning radius of around 90km, and that’s still probably generous. By the time you turn, your slower opponent will have vectored towards you and lined you up with a long-range missile, which is faster that Mach 4.

Fighters can’t dogfight at Mach 4, and they can’t manage that performance at low altitudes either.

The idea is that a plane with Mach 4 capability can cover more ground and be staged farther away from its ultimate target. It can get there faster, or get out of the area faster if the odds aren’t good. But it won’t be highly maneuverable at those speeds.

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