The U.S. Merchant Marine “Civilian” Warships of World War II and their Armament

By James V. Shannon
Updated 10 July 2002

When we think of armed merchant ships, we often think of two centuries ago, or more.  Perhaps as far back to the days of The East India Company, when their ships were armed with cannon to fight off privateers and pirates.  And of those privateers, whose civilian owners could petition for Letters of Marque from a country’s government, which licensed them to prey on “ships of the enemy” in wartime, sharing their gains with the government.

But in World War II, in the mid-twentieth century, the United States armed its merchant vessels, often with more armament than the Navy and Coast Guard escort vessels that guarded their convoys.  And yet they were “civilian” ships, manned by “civilian” crews.  The United States Merchant Marine was a critical element in the Allied forces seagoing operations of World War II.  These ships carried the bulk of all material sent overseas, and many of the men who served there.  A loaded merchant ship was a target worth more than a corvette, or a destroyer escort, or even a destroyer; perhaps more than a light cruiser to the German submarines in the North Atlantic.  Sinking a loaded merchant ship denied the Allies her cargo for the combat theaters.  Loaded or empty, sinking her prevented her from carrying additional vital cargoes.  The Merchant Marine suffered the highest rate of men killed in action of all of the Armed Services, even the U.S. Marine Corps.

At the outset of our participation in World War II, all merchant ships were requisitioned by the U.S. Government, placed under control of the War Shipping Administration (WSA) and fitted with armament, armor, and countermeasure equipment such as degaussing.  The WSA assumed responsibility for the ships should they be damaged or sunk, and contracted with qualified shipping companies to operate them.  Cargo assignment and routing was provided by the U.S. Navy.

The merchant ships carried a Navy Armed Guard contingent of one officer and about twenty men to operate and maintain the guns, although they were often short of that complement.  The gun crews were filled out with civilian crewmembers, sometimes including ship's officers.

Initial armament was by guns drawn from the stored weapons from World War I.  Emphasis was on the stern weapon, often a 4 inch 50 caliber gun, supplemented with a lighter caliber gun in the bow and machine guns of .30 and .50 caliber distributed about the ship, such as on the flying bridge.  When more suitable weapons became available as weapon production ramped up, these lighter weapons were replaced with heavier and more modern equipment.

The Liberty Ship was the most numerous ship design in sea service, with over 2,700 built during World War II.  It can serve as the prime example of the armed merchant ship and its weapons.

Armament was typically one 5 inch 38 caliber gun on the stern; one 3 inch 50 caliber gun in the point of the bow; a 20 mm Oerlikon machine gun on each of the four corners of the flying bridge (the open top deck of the midship house); and two 20 mm Oerlikon guns, one on the end of each wing of the after steering station atop the poop house.  All of the guns were mounted in circular gun tubs about waist high protected with plastic armor.  This gave a total armament of one 5 inch, one 3 inch and six 20 mm weapons.

Plastic armor was composed of a bituminous (blacktop) matrix impregnated with stones.  It was invented by the British to replace expensive and scarce steel armor.  Plastic armor was also used to protect the bridge and radio room of merchant ships.  Troop Transport Liberties, which were fitted out to carry 500 troops plus their combat equipment, retained the 5 inch 38 caliber gun on the stern and the 3 inch 50 caliber gun on the bow.  The 20 mm Oerlikon guns at the after steering station were replaced by two 3 inch 50 caliber guns.  Two 20 mm Oerlikon guns were added on the foredeck and two more on the afterdeck, all in raised gun tubs and intended to supplement the four 20 mm guns on the flying bridge.  This provided a total armament of one 5 inch, three 3 inch, and eight 20 mm guns.  There was no fire control equipment; engagement was over open sights under the direction of the Armed Guard Officer whose action station was on the bridge.

A merchant ship is required to post a notice called the “Station Bill” that lists each crewman’s position and his station while on watch, and his station and duty during an emergency; such as, “Third Mate, Watch Station - Bridge, Emergency Station - Bridge, assist Captain.” In wartime, gun crew stations were also listed and assigned to civilian crew members.  Volunteers for service in the Merchant Marine were trained by the U.S. Maritime Service under the War Shipping Administration, a quasi-military organization modeled after the training organization of the U.S. Coast Guard.  In basic training – boot camp – these recruits were given brief training to teach them how to serve in the gun crew at all positions except gun captain, and the gun aiming positions for azimuth and elevation.  In advanced training, such as that for Radio Officers, lessons in aiming the weapon were added.  On shipboard, gun crew assignments were generally as ammunition passers and loaders.  They were also competent to assume the duties of disabled Navy gun crewmen, and to fill out shortages in the other positions of the Armed Guard gun crews.

These ship's armament was meant to be defensive in nature.  The standing orders for a merchant ship in combat with a surface ship or surfaced submarine were to turn away, put the attacker on the stern and run (or, when feasible when in contact with a surfaced submarine, to ram him.) Thus, the heaviest armament was on the stern with the tactical intention of discouraging pursuit.  However, one Liberty Ship, the SS Stephen Hopkins, shot it out with the German auxiliary cruiser ("merchant raider") Stier and the supply ship Tannenfels, sinking the former and damaging the latter.

The guns were dual purpose and sited to provide maximum coverage against attack from any direction.  The most common engagement was against attacking enemy aircraft, where they gave a good account of themselves.

Further information may be found at this US Navy Historical Center FAQ.



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