12"/45 caliber Mark 5 gun

• Name — 12-inch/45-caliber Mark 5 Naval Gun • Origin — United States • Is Ranged — YES • Is Artillery — YES • Service — 1906–1930 • Used By — *United States Navy • Greek Navy • Wars — *World War I • Russian Civil War • Greco-Turkish War • World War II • Designer — Bureau of Ordnance • Design Date — 1903 • Manufacturer — U.S. Naval Gun Factory • Part Length — bore (45 calibers) • Rate — 2–3 rpm • Elevation — −5° to +15°

The 12 in/45-caliber Mark 5 naval gun was designed as an incremental improvement upon the preceding American naval gun, the 12-inch/40-caliber gun Mark 4. As such, it was a very similar weapon, having been lengthened by 5 calibers to allow for improved muzzle velocity, range, and penetrating power. Designed to the specifications of the Bureau of Ordnance, the Mark 5 was constructed at the U.S. Naval Gun Factory in Washington, D.C.

The Mark 5 weighed and was capable of firing 2 to 3 times a minute. At maximum elevation of 15° it could fire an shell approximately. However, this range was largely academic at the time the gun was initially designed, as no rangefinding techniques had yet been developed capable of accurately firing beyond about. With an initial muzzle velocity of, the gun had a barrel life of 175 rounds, and was capable of firing either armor-piercing or common projectiles. As designed, the Mark 5 was capable of penetrating of Harvey plated side armor at, at, and at. By comparison the 12-inch/40-caliber Mark 4 it replaced could only penetrate, and at those distances, respectively.

• Illustration — After six Mark 5 guns aboard USS Delaware, c. 1913. The Mark 5 entered service in 1906 and remained the primary battleship gun for all American battleships commissioned before 1912, at which point it was replaced by the 12"/50-caliber Mark 7. All told, the Mark 5 would arm 14 battleships of five different classes, making it the most-used main gun in American battleship history. Despite this distinction, the only Mark 5 guns ever to be fired in anger were actually in Greek, and not American, service. The ex-s and, sold to the Royal Hellenic Navy in 1914, fought in both the Allied Intervention in the Russian Civil War, and the Greco-Turkish War. Though during World War I the Mark 5 would cross the Atlantic for duty aboard two of the American battleships serving in the 6th Battle Squadron of the Grand Fleet, it was never fired in any engagement, as no battles were fought with the German High Seas Fleet in 1918. The five classes armed with the Mark 5 were: In American service, the Mark 5 remained afloat (albeit in dwindling numbers) until 1930, when the last guns were removed from the Floridas in compliance with the terms of the London Naval Treaty.

A Mark 5 Mod 8 gun is displayed at Fort Hamilton in Brooklyn, New York, representative of the general type of coast artillery guns the fort had.

• Illustration — View looking aft along the port side, showing barrel of burst 12-inch gun on deck with the gun's rear portion in Turret # 2. Photographed at the Philadelphia Navy Yard, Pennsylvania, 25 September 1916. Note holes in superstructure and in the "cage" foremast caused by this accident. During the summer of 1916, Michigan blew out her left hand gun in turret No. 2 during target practice. After an investigation of South Carolinas guns it was discovered that copper deposits from the driving bands on the projectiles had narrowed the bores of the barrel enough that it caused the projectiles to slow down. This problem, known as "copper choke", allowed the pressure in the barrel to increase to dangerous levels. Lapping heads, to remove these deposits, were issued for all guns 12-inch and larger throughout the fleet. The lapping heads were later replaced by wire and pissaba brushes.

Following the signing of the Washington Naval Treaty in 1922, many of the Mark 5 guns in service were removed from sea duty and transferred to the U.S. Army for use as coastal artillery. In this capacity, the maximum range of the Mark 5 increased to, due to the greater elevation that was possible. These guns were not deployed by the US Army, and some were sold to Brazil, where they might still be in use. In Greek service, the guns removed from Lemnos were emplaced on the island of Aegina, where they helped to defend the approaches to the port of Athens.

• 305mm/45 Modèle 1906 gun – French equivalent • BL 12-inch Mk X naval gun – British equivalent • EOC 12-inch 45-calibre naval gun ("41st Year Type") – British-manufactured Japanese equivalent