However, this 600 casualty number should be taken with a very large grain of salt ... A lot of Russian dead, but 600? That is either garbage or the luckiest shot of the war.
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Luck had nothing to do with it - mobniks need to be kept together or lose controls over them.
They were all housed in one building with artillery shells, rockets, and powder stored in the basement. There is nothing unusual about this for the modern Russian army. They’ve lost other much smaller groups this way. With this hit, its over 1,000 dead for the week by similar strikes.
The building was located only 20 miles from the front. When it was hit at one minute after midnight, every one was likely asleep. We don’t know how many rockets hit but a salvo of 6 could easily penetrate to the basement, striking the powder and rockets.
Russian Mil bloggers also say the number of dead is in the hundreds. There would have been no warning, first because Russia withdrew its air defenses to Moscow-St Petersburg, and second, because of the very short distance from the front.
Pile 600-700 people into one building with ammo stored underneath a short distance from the front and you get a lot of dead in one go.