As good as HIMARS are, their explosive payload is not large enough for concrete bridges. You need a truck bomb to do this at Kerch. To collapse 2-3 spans. And this is how it was done. A truck laden with C4 / Semtex whatever, compact effective explosives.
The driver was a Ukrainian or Russian with terminal illness.
As a former artillery officers, HIMARS are not subtle, either.
You would know they were the weapon, especially in a quiet area. Long plume of smoke, fire, etc.
Hitting a moving truck on a bridge going 60mph without laser guidance/spotter would be a heck of a lucky shot.
On the other side of the argument, the precision warhead has a 91kg (about 200lbs) warhead. Coming in fast, a typical cluster could easily do this damage. (We didn’t typically fire one, but 2-3 or 5. With a critical target like this bridge, we’d have opened up.)
The driver was a Ukrainian or Russian with terminal illness.
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The driver was a very healthy guy with a remote, handling a sea drone laden with several thousand pounds of explosives.