Most combat aircraft fall into one of several conventional categories: fighter, bomber, ground attack airplane. The M-25, or “Theme 25”, designed by Soviet Myasishchev aircraft construction bureau between 1969 and 1972, did not. It was an attack aircraft designed to employ a completely new kind of warfare: destroying enemies with its sonic boom.

The story begins in southwestern Russia in the closing months of 1978. A lone MiG-21S Fishbed fighter jet screams in cold, dry air above farmland near Lipeck, gaining speed as the pilot pushes the throttle grip. He reaches the border of large proving ground, nudges the flight stick gently forward and levels at the altitude of a couple dozens of meters. The afterburner kicks in. The jet goes supersonic.

Massive shockwave echoes above the barren frozen ground, with chunks of dirt and dried grass flung high up into the air, trailing behind like a sideways hurricane. As any MiG pilot would tell you, a fighter becomes a bomber at supersonic speeds: you are flying on rails, the flight stick is “rubber”, even the minutest maneuver strains the airframe immensely. The further the deadly ground is from you, the better. But secret military experiments are not meant to be safe.

Several sensors are scattered on the ground in the flightpath of the MiG: narrow steel tubes, similar to metal pens, fixed on bench-like stands made of roughly welded tubing. They shake as the plane swoops above and the result is registered.

Half a year passes, and on June 17, 1979, Vladimir Vasilyevich Struminsky – the director of the Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Academy of Sciences of the Union of Soviet Socialist Republics – walks through the corridor of Ministry of Aviation Industry in Moscow. He is a tall, fit man with hawkish facial features, incredibly long job title and a folder marked “Top secret” in his hands. The folder contains the report on earlier experiments, as well as the Ministry council’s decision on a new project proposal: to start the development of “Theme 25: special-purpose sonic wave ground attack aircraft”.

MiG-21 low-level supersonic flight experiments, conducted in a remote proving ground, were a joint effort of the Institute and the Soviet Air Force, ordered by the Ministry. The reason for such an order is not entirely clear and contains a mystery in itself. But the result was definitive: Struminsky would be provided funding, manpower and connections to go on and develop the “Theme 25”. Although the maximum pressure MiG-21 sonic boom generated was 0.05 kilogram-force per square centimeter – 0.7 psi, enough to shatter window glass, but barely anything more – the concept proved promising enough.

MiG-21 in flight AeroTime News

Mikoyan-Gurevich MiG-21 Fishbed in flight (Image: Cory McDonald / Wikipedia)

Of course, the MiG-21 is a very aerodynamic aircraft, designed to have minimal drag, which means minimal sonic boom too. To have a more powerful sonic boom you have to have an airplane which is way less aerodynamic. The aircraft shape is even more important, as it is possible to focus the sonic boom by generating it with flat surfaces, instead of round cross sections of fuselages of regular planes. According to Struminsky’s research, some modifications to the MiG-21 airframe would increase the shockwave by 5-6 times, pushing into the territory of 5 psi – enough to collapse buildings and cause fatalities. 

But in order to make such an unaerodynamic aircraft supersonic, you need some colossal thrust. On top of that, aircraft's structure will have to endure all the drag, and the heat that comes with it. To really weaponize a destructive force of a sonic boom, a special, extremely sturdy airframe is needed, and stupendously powerful engines to go with it.