Anti-submarine net

The US Navy used anti-submarine nets in the Pacific War to protect major US Naval Advance Bases.

Because they were a reaction during the war, there was not time to study the best construction methods, or the nets' overall efficacy.

While a boom blocks a waterway for surface ships, a submarine net does the same below water.

The most extensive use of anti-submarine nets during WWI was the Dover Barrage, spanning the English Channel.

[citation needed] Scapa Flow is a large natural harbor in Scotland.