Drownings galore in rivers, lakes and mill ponds, but no military connection, I'm afraid;
Twa Sisters
Marrowbones
Drowned Lovers/Clyde's Waters
Annan Water
Lakes of Shilin

(And how strange to think that Nic Jones was once a lifeguard at Chelmsford Swimming Pool.)

Plenty of sailors drowned in storms at sea;
Drowned Sailor
Sir Patrick Spens