Too bad there's that pesky radiation that doesn't just go away after a few seconds...
I actually at first got the idea that the team operating the gun would be caught in the blast of the detonation themselves, at least that would have been a quick death.
Nah, the blast's not much of a problem. The Davy Crockett has a range of up to 4km, for a warhead of that small yield the blast is ok.
But the initial flash and residual radiation is still significant.