As usual, the Germans were first, with the V-2 reaching Mach 5 in the 1940's, which was to an extent controllable (they landed in England.) For an airplane to

As usual, the Germans were first, with the V-2 reaching Mach 5 in the 1940's, which was to an extent controllable (they landed in England.) For an airplane to reach Mach 1, this mainly requires thin wings and enough power/dive. To control it, you need a flying tail, and swept wings and "waisting" the fuselage reduces the amount of power needed. So almost all of the planes in WW2 were "too thick" and incapable of supersonic flight, though could have exceeded Mach 1 with modified wings, tail and in a dive. The US P-80 (1945) and F-86 (1949) jets had underpowered engines, in the sense that all early jet engines had limited power. However the F-86 had swept wings, and later versions of the F-86 had a flying tail, so if you pointed it at the ground, you could get a sonic boom without losing control. Source: I study aerodynamics.