page_title: Defensively equipped merchant ship
section_title: United States
hierarchical_section_title: Defensively equipped merchant ship / United States
caption_attribution_description: English: The Mark 37 Model 6 5-inch dual purpose gun on display at the National Museum of the Pacific War in Fredericksburg, Texas, United States. The gun had a range of over 6 miles and could fire 22 rounds a minute.
context_page_description: Defensively equipped merchant ship was an Admiralty Trade Division programme established in June 1939, to arm 5,500 British merchant ships with an adequate defence against enemy submarines and aircraft. The acronym DEMS was used to describe the ships carrying the guns, the guns aboard the ships, the military personnel manning the guns, and the shore establishment supporting the system.
context_section_description: The Merchant Marine Act of 1936 identified mariners aboard United States flagged merchant ships as military personnel in time of war. Neutrality Acts prevented arming of United States flagged merchant ships until 17 November 1941, although American-owned ships under Panamanian registry had been armed earlier. Guns were manned by United States Navy Armed Guard. The United States began equipping ships of other nations with guns and United States Navy Armed Guard on 24 January 1942; and approximately 145,000 USN armed guards ultimately sailed aboard 6,236 merchant ships. United States policy was stated by the Vice Chief of Naval Operations on 19 August 1942: "Ships sailing independently should be armed.  Ships sailing in regularly made-up convoys, other than ships bound to North Russia or tankers en route to the United Kingdom, may sail unarmed if the urgency of delivery of their cargo warrants it."
  The United States followed the British practice of a single large gun aft.  Early United States installations included low-angle 4"/50 calibre guns (Mark 9) removed from old Wickes-class destroyers and Clemson-class destroyers. The first installations of dual-purpose 5"/38 calibre guns began in September 1942, on new ships over 10,000 tons. Victory ships carried a 3-inch gun on the bow, 20 mm machine gun tubs port and starboard between the first and second holds; a second pair of 20 mm guns on the bridge wings, a third pair on the after edge of the superstructure, and a fourth pair between the after (Number 5) hatch and the 5"/38 calibre gun on the stern.
caption: 5"/38 calibre dual-purpose Mark 37 gun mount used on American merchant ships. This example is preserved at the National Museum of the Pacific War.
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