The primary armament of the SS Jeremiah O’Brien during the Second World War was two, 3-inch 50 caliber Naval guns mounted on the bow and stern gun platforms. These guns were intended for defense against aircraft, ships, and surfaced submarines and had a range of approximately ten miles.
The 3” guns were each manned by a crew of eight members of the Naval Armed Guard. The forward gun crew was quartered in the main house next to the officers’ mess and the aft gun crew was quartered in the Aft House located below the Aft Gun Platform.
If cargo was carried on the main deck, wooden catwalks were built for the gun crew to quickly access their battle stations. Ammunition for each station was brought up by a hoist from their respective magazines below the main deck and trained Merchant Mariners were assigned battle stations to complete the crew, whenever necessary.
All of the O’Brien’s guns were removed in 1946 by the U.S. Navy prior to the ship being placed into the reserve fleet at Suisun Bay. During the ship’s restoration in 1979, they were replaced with 3-inch and 5-inch guns salvaged from the US Navy commissioned Liberty Ship, USS Palawan that was sunk off the San Diego coast to create an artificial reef.
There were many models and variations of the 3” gun produced, with some models still in use today. The O’Brien’s current 3-inch gun is a Mark 2, Model 4 manufactured by General Motors, Fisher body division.
Explore this Station's Gallery
Descend the gun platform. The O’Brien’s pin-up gal, Miss Jerri O’Brien, is painted on either side of the gun platform’s walls and can be viewed by looking up from the bow.