Also, I think I remember reading that to fire a Glock underwater, you need to have special/replacement plastic cups/collets that hold the firing pin/spring in place. The cups have cut-outs that allow any water in the firing pin channel to get out of the way as the firing pin is trying to strike the primer. If trapped water is not given an escape route, it will slow down the firing pin significantly and may not fire the round.
I just do not understand why someone would attempt firing a firearm underwater.
If the firearm exploded. I wonder who they would blame and attempt to "SUE".
They had to get so close. A hand held harpoon would due.