Use of the Jolly Roger by submarines

The Jolly Roger is a symbol that has been used by submarines, primarily those of the Royal Navy Submarine Service and its predecessors. The practice came about during World War I: remembering a 1901 complaint by Admiral Sir Arthur Wilson that submarines were "underhanded, unfair, and damned un-English" and that submarine personnel should be hanged as pirates, Lieutenant Commander Max Horton began flying the flag after returning from successful patrols.

Source: Wikipedia — Use of the Jolly Roger by submarines (CC BY-SA 4.0)