I remember being astounded by how the water "amplifies" the explosions - so while a hand grenade blast is very dangerous on the surface, under the sea it becomes far more horrific prospect, due to the water transferring the blast more efficiently. Nerve wracking stuff, when you're thinking about diving down there - imagining that a bomb dozens of meters away could pulverize you.
Still pretty rare, thankfully. I applaud the diver bomb disposal squads - some of the most dangerous work there is.