[jjm2111]

I know of no current navy brownwater platform that carries a mortar. Like you said, not very stable, plus the boat would be moving too fast to aim a mortar properly. BUT.....

1. I'm way young, so it coulda happened in NAM.

2. People augment all sorts of shit, so it may not have been standard issue.

[Paratrooper]

It was not a mortar round, it was most likely a M240 Grenade launcher. I have a friend who had a similar experience with a grenade launcher. He was a LT in the infantry basic course at Ft Benning and the class was shooting the grenade launcher at night on a range. He aimed his weapon to high in the air and when he fired he hit tree limbs. The round went off and a small piece...a sliver of metal hit him in his privates. He bled some and they took him to the medic. There was no damage done other than this small piece of metal lost some where in his sack. It was never removed and sometimes when he crosses his legs he gets a get a sudden stick like a needle prick to his privates. He later had two boys so all still functioned properly.