12"/45 caliber Mark 5 gun

The 12"/45 caliber Mark 5 gun was a US naval gun that first entered service in 1906. Initially designed for use with the  of pre-dreadnought battleships, the Mark 5 continued in service aboard the first generation of American dreadnoughts.

Design and development
The 12"/45 caliber Mark 5 naval gun was designed as an incremental improvement upon the preceding American naval gun, the 12"/40 caliber 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.

Measurements and Capabilities
The Mark 5 weighed 53 tons and was capable of firing 2 to 3 times a minute. At maximum elevation of 15° it could fire an 870 pound shell approximately 20,000 yards. 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 10,000 yards. With an initial muzzle velocity of 2,700 f/s, 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 16.6 inches of Harvey plated side armor at 6,000 yards, 12.2 inches at 9,000 yards, and 9.9 inches at 12,000 yards. By comparison the 12"/40 caliber Mark 4 it replaced could penetrate 14.6 inches, 11.6 inches, and 9.4 inches at those distances, respectively.

Naval Service


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-utilized 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-Mississippi class battleships Kilkis and Lemnos, 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.

Coastal Artillery
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 30,000 yards, due to the greater elevation that was possible. These guns protected the Panama Canal Zone through World War II, after which some were permanently retired and some were sold to Brazil, where they might still be in use. In Greek service, the guns removed from the Lemnos were emplaced on the island of Aegina, where they helped to defend the approaches to the port of Athens.

Weapons of comparable role, performance and era

 * 305mm/45 Modèle 1906 French equivalent
 * BL 12 inch Mk X naval gun British equivalent
 * Type 41 12-inch (305 mm) /45 caliber naval gun Japanese equivalent