20 were lost from a cause unknown. In other words, they went on patrol, and nothing more was heard of them. The enemy have no knowledge of their fate, and there were no survivors from them. Their loss was probably due to their striking mines.
5 were sunk by enemy submarines (one of them—"E 20"—in the Sea of Marmora).
3 were sunk while entering the Dardanelles, and 1 by gun-fire in the Marmora.
4 were sunk by mines off our own coasts.
3 were wrecked on neutral coasts, 1 in the Baltic, and 1 on our own coast.
2 were sunk by air bombs.
7 were sunk by collision.
3 were sunk in error by gun or ram by our own side.
1 sank in harbour, 1 sank on trials, 1 was sunk by gun-fire after sinking a German destroyer off the Bight, and "C 3" blew herself up on St George's Day against the Mole at Zeebrugge.
The losses were heavy, but were not incurred uselessly. The boats were the outposts of the Fleet, and, however great the losses, they could never have equalled those the bigger ships would have had to endure had they been given the same patrols to perform.