Surface-to-air and air-to-air missiles are fast, but with short range. For any fuel-burning aircraft there's a tradeoff between size, speed, and range. If you w

Surface-to-air and air-to-air missiles are fast, but with short range. For any fuel-burning aircraft there's a tradeoff between size, speed, and range. If you want Mach 3 and intercontinental range, you need something huge and expensive like an SR-71. Nuclear ramjets, if they can be made to work, could be both hypersonic and very long range. Very long range is important because you can launch them early in a conflict and have them cruise around, safe from incoming tactical nukes destroying your launch sites.