3"/50 Calibre Gun (Mk 22, Mod 0)

Crew training in Dam Neck, VA on 3 August 1942. 
National Archives #80-G-10276.

3"/50 on display at the USS Bowfin museum in Honolulu, HI.

    Although the 3"/50 calibre was an excellent anti-aircraft weapon, it proved to be too light to be effective against surface targets, and in 1942 was replaced by the heavier 4"/50 Mark 12 gun. As a direct fire weapon, the small 13 pound projectiles used in the 3"/50 had a reputation of bouncing off U-boats and merchant vessel light plating. As an AA weapon, the tiny HE payload and relatively low rate of fire made the weapon almost useless against fast-moving aircraft.  On April 6, 1943 the British Frigate Goodall (K-479, the former Evarts-class DE-274) attempted to scuttle a damaged tanker by firing 36 rounds of armor-piercing ammunition into the light-plated hull. The gunnery officer observed at least 20 ricochet off without penetrating. Frustrated with the 3"/50's performance, the crew finally sank the tanker with shallow depth charges.

    There are also many colorful stories about a design defect in the breech block that plagued the 3"/50 throughout its service life. The firing pin is enclosed within the breech block, which is pulled away from the breech to insert a projectile.  When the breech block was closed, the weapon had a reputation for firing, regardless of whether the trigger was pressed.  The Navy ordnance publications recognized this problem and recommended lubricating the firing mechanism with light machine oil instead of grease.  Nevertheless, the reputation for premature firing stuck with the 3"/50 until the end of its service life.

    The term "calibre" is used to describe ammunition. It is a relationship between the diameter of the projectile and the length of the gun tube. A 3"/50 calibre gun fired a 3" diameter projectile through a rifled tube 150 inches (3x50) long. Other examples are: 5"/38 commonly found on DDs, 5"/25 on submarines, and the giant 16"/50s found on battleships.  The projectiles are not interchangeable among the same calibre, i.e. a 5"/38 projectile cannot be used in a 5"/25 tube. Today, the U.S. Navy is the only service still using this naming system.

    Guns 5" and smaller were housed in "mounts". Guns 6" or larger are housed in "turrets".  Most Destroyer Escorts had three 3"/50 open mounts. The one piece rounds were stored below decks in "Ready Boxes" near each mount. Each round weighed approximately 25 pounds and was hand loaded by a man chosen for his strength. When the gun was fired, a "Hot Caseman", wearing asbestos gloves, kept the empty brass from interfering with the loader who immediately loaded the next round. The 3"/50 guns on DEs were manually operated by pointers and trainers who cranked the guns into firing position by "matching pointers" on dials controlled by the Mark 52 gun director. Some later DEs were upgraded to the 5"/38 guns in modified, enclosed mounts. The 54 pound projectiles and 28 pound powder bags were brought up from below the mount and the guns were positioned by either hydraulic or electric drives. The first centerline mount is #1 and so forth. The most forward 3" mount would be 31, the next 32, and so on. 40mm mounts would be Mount 40-1, mount 40-2 and so on. Mounts not on the centerline are designated by even numbers on port and odd numbers on starboard. Thus the most forward 40mm mount on the starboard side is mount 41 and first one on the port side is mount 42. A single 40mm on the centerline would be mount 40. The 20mm mounts had similar designations. Usually guns 40mm and larger had a direct phone line to the bridge.