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I was watching a video about "The Big Stick" aka Project Pluto, a nuclear powered SLAM. In the video (I couldn't find the exact video) it said that after deploying its weapon payload a SLAM could fly over its target country as a "vengeance weapon", causing destruction with it's sonic boom for weeks and an altitude of just a few hundred feet.
What kind of damage would a mach 3 flyby at 200 feet cause?
I'm interested in both building damage and possible human injury.
The video is highly inaccurate in that area.
The actual damage the missile would have caused would have been largely radiological, from ejected radioactive material in its exhaust plume.
While windows and weak structures may receive damage from extremely low flying Mach 3 bodies, this would probably be limited to say some broken glass.
The plan was also never really considered. What was considered is having the weapon, now without its warheads, fly to a final target area and do a high speed dive into the ground, the kinetic energy alone combined with the spread of radioactive material from the rupturing nuclear reactor causing the damage there.
Mind that the damage (both physical and radiological) of the weapon flying overhead isn't clear. Different sources list different predictions. Some way the damage would be minor, others that it would be severe. But rest assured, the noise would shatter eardrums, the supersonic shockwave flatten crops and lightly constructed buildings, and the radioactive exhaust plume wouldn't have been healthy either.
I've always found this to be an excellent article on the project and the people surrounding it.
Edit: a very interesting article by the designer of the reactor about the problems inherent in the reactor design, and how he thought about the radiation hazard for people on the ground working with the missile: Merkle public paper
Unrelated to the nuclear ramjet aspect, a close high-Mach flyby has many of the same effects as an explosion. The shock wave has a pressure profile very similar to the "N wave" of an explosion -- positive overpressure followed immediately by a vacuum underpressure -- and depending on the shape of the supersonic object, there may be multiple overpressure waves.
Historically, sonic booms were fairly common when I was a child, if you lived close to an Air Force Base; I grew up about 150 km from Fairchild AFB (Spokane, Washington) and used to hear the booms once or twice a week. This was in the 1960s, before the ban on non-emergency supersonic flight over populated areas.
Even with an aircraft flying at high altitude (FL200, at a guess), these booms could and would rattle windows; they were loud enough to startle people, sometimes leading to kitchen injuries (dropping hot items, for instance) or falls. Given that the intensity of the pressure wave from a linear source like this obeys an inverse law, such a boom (from aircraft that were only low supersonic, probably Mach 1.1 to 1.2) from a hundred times closer would be a hundred times stronger -- and go from rattling windows to breaking them, flying glass injuries, many falls (people knocked off their feet by the pressure, never mind off ladders), and so on.
Look at the damage at Chelyabinsk from their bolide explosion a few years ago -- while that object was, well, rock-shaped, at high altitude and much higher speed, that's the kind of damage you might expect with a fairly close supersonic flyby of a streamlined aircraft or missile.
