Net laying ship

1930s

War Plan Orange, the pre-World War II US plan for war with Japan, anticipated that Pearl Harbor would be too small for the US Navy fleet that would be amassed in Hawaii. Orange anticipated the construction of a large anchorage in Lahaina Roads between the islands of Maui, Lānaʻi, and Molokaʻi. Construction would consist of massive nets and minefields to protect the anchored ships.

Changing requirements

Ultimately four large netlayers would be laid down just before and after the attack on Pearl Harbor: USS Monitor, USS Montauk, USS Osage, and USS Saugus. It turned out that these ships were not needed. First, dredging significantly enlarged the anchorages in Pearl Harbor. Second, the mobility of aircraft carrier warfare made the large Lahaina Roads anchorage concept obsolete, though smaller nets would still be needed for the entrance channels at advanced bases such as the Naval Base Majuro and Naval Base Ulithi. Third, new technology resulted in lightweight nets that could be handled by smaller vessels. The four large netlayers would be converted to carry and launch amphibious vehicles under the hull classification landing ship, vehicle (LSV).

1940s

The 77 small auxiliary net layers were built in three classes. The first 32, the Aloe class, were all launched in 1940 (before the attack on Pearl Harbor) and were built of steel. Due to the chronic shortage of steel during the war, the next 40, the Ailanthus class, were built of wood. The last 15, the Cohoes class, laid down in 1944 and 1945, were again constructed of steel. These vessels served in all theatres of war but particularly in the Pacific. Many of the ships were decommissioned after the war, but some continued in service for several more decades. Net layers were eventually made redundant by advances in underwater detection technology.

There were also at least 43 craft that were classed as net gate craft; many were simply powered barges.

To transport nets and to otherwise support the net layers, by 1943 specially built cargo ships, designated net cargo ships (AKN), were built. The first of this class was USS Indus. Indus worked in Naval Base Philippines. Finally in 1946, USS Montauk was converted back from an LSV to net cargo duties as USS Galilea.

The United Kingdom and British Commonwealth referred to net laying ship as boom defence vessels.

• Bar-class boom defence vessel built in the 1940s.
• Net-class boom defence vessel built in the 1930s.