We have said before on this site that some of the West's weapons during the Cold War were not so hot, eg the 1954 vintage F-100 Super Sabre with a 39% accident rate, and 324 pilots killed. Although it could exceed Mach 1 in level flight it was nevertheless under powered at 10 000 lb static thrust. On landing it could get into a situation that the pilot could not rectify, and crash. See https://www.youtube.com/watch?v=Q2qqKwndFW0
If the angle of attack was slightly too much, lift was lost at the wingtips of the sharply swept wings. This moved the centre of pressure forward, lifting the nose even higher. The engine did not have enough thrust for the aircraft to climb out of trouble and so it would crash, the hapless pilot being unable to do anything about it. The contemporary British BAC Lightning fighter had a somewhat better flight envelope due to the 24 000 lb thrust from its two engines, mounted unusually one above the other. On the other hand, the British Swift and Javelin fighters were also poor performers.
Both sides in the Cold War tried to hide their mistakes. Only after the end of the Cold War has such information as we quote above has become available.