12 inch/50 Mark 7 gun

• Name — 12"/50 caliber Mark 5 Naval Gun • Origin — United States • Type — Naval gun • Is Ranged — YES • Is Artillery — YES • Service — 1912-1952 • Used By — * United States Navy • Argentine Navy • Wars — *World War I • World War II • Designer — Bureau of Ordnance • Design Date — 1910 • Manufacturer — *U.S. Naval Gun Factory • Bethlehem Steel • Number — *Mod 0: 28 (Nos. 180–182, 186–210) • Mod 2: 3 (Nos. 183–185) • Mod 3: 6 (Nos. 211–216) • Export: 25 (Nos. 795–817, 919–920) • Variants — Mods 0–19 • Weight — * (without breech) • (with breech) • Part Length — bore (49.5 calibers) • Cartridge — armor-piercing • Rate — 2–3 rounds per minute • Velocity — * (full charge) • (reduced charge) • Range — at 15° elevation • Elevation — -5° to +15° • Traverse — −150° to +150°

The 12 in/50 caliber Mark 7 naval gun was only a slight improvement over the preceding American naval gun, the 12"/45 caliber Mark 5 gun. As such, it was a very similar weapon, having been lengthened by five calibers to allow for improved muzzle velocity, range, and penetrating power. Designed to the specifications of the Bureau of Ordnance, the Mark 7 was constructed at the U.S. Naval Gun Factory in Washington, D.C. The Mark 7 weighed with the breech and was capable of firing two to three times a minute. At maximum elevation of 15° it could fire an shell approximately. With an initial muzzle velocity of, the gun had a barrel life of 200 rounds, and was capable of firing either armor piercing or Common projectiles. As designed, the Mark 7 was capable of penetrating of Harvey plated side armor at, at, and at. By comparison the 12"/45 caliber Mark 5 it replaced could penetrate, and at those distances, respectively. Bethlehem Steel built the first gun, No. 180. Mod 0, Nos. 181, 182, and 186–200, was a built-up gun consisting of a tube, jacket, and eight hoops, a screw-box liner with locking hoops and rings and hand operated and Smith-Asbury mechanism. The gun was constructed with nickel-steel and hooped to the muzzle. Mod 1 was gun No. 180, rebuilt into gun No. 180L, with its chase hoops rebuilt along with a new conical nickel-steel liner, a smaller chamber, and the rifling increased. Mod 2, gun Nos. 183–185, was a Mod 0 gun relined with a conical liner, a new chase locking hoop, and with a locking ring added. This brought the weight up to 125498 lb, with the breech. It also had a 25 cuin-smaller chamber. The Mod 3 guns, Nos. 211–216, were the last new guns built, all other Mods were Mod 0, 2, or 3 guns that were modified. These guns were built with a new simplified design, no liner, five hoops, a locking ring, along with a screw-box liner and a different gas check seat. Mod 4, the twelve guns from Wyoming, relined in 1921–1923, had a conical one-step liner and uniform rifling with a new chase locking hoop and locking ring. With the Mod 5 an attempt was made to reline a Mod 1 with a uniform twist rifling, but it was dropped. Mod 6 relined Mod 2 with a uniform twist rifling along with a modified new chase hoop and locking ring. Mod 7 took the Mod 3 and used a one-step conical liner, uniform twist rifling, and added a tube and liner locking ring. Mod 8 was the Mod 0 or Mod 4 also using a one-step conical liner, uniform twist rifling that was secured by a tube and liner locking ring with a liner locking collar at the breech end. The Mod 8s that used Mod 0 guns also added a new chase hoop and locking ring. Mod 9 was a Mod 2 or Mod 6 that had a new liner with longitudinal clearances at the liner shoulders installed, uniform twist rifling along with a tube and liner locking ring and collar added at the breech end. Mod 10, like the Mod 9, was also a Mod 2 or Mod 6 that had a new liner with longitudinal clearance at the liner shoulders installed, uniform twist rifling along with a tube and liner locking ring and collar added at the breech end. The Mod 10 used Breech Mechanism Mark 9 instead of the Mark 8 on the previous Mods. Mod 11 was a Mod 7 that had the chamber lengthened, adding cuin, and a 3½° breech band seating slope and used Breech Mechanism Mark 12. Mod 12 used a Mod 10 and lengthened the chamber and added a 3½° breech band seating slope with Mod 13 being similar but of a Mod 8, Mod 14 used a Mod 9, Mod 15 used a Mod 7, Mod 16 used a Mod 10, Mod 17 used a Mod 8, and Mod 18 a Mod 9. Mod 19, the last modification, used a Mod 2 with its breech modified for the Smith-Asbury Breech Mechanism and the forward end of the chamber modified similar to the Mod 18, lengthened the chamber and added a 3½° breech band seating slope. The breech end was further modified by being machined out so that it could accommodate a gas check seat liner locking ring. The Mod 19 could also be used right or left handed by cutting a new slide keyway that was 180° from the original keyway.

• Ship — Gun Installed — Gun Mount • Wyoming — Mark 7: 12"/50 caliber — Mark 9: 6 × twin turrets • Arkansas — Mark 7: 12"/50 caliber — Mark 9: 6 × twin turrets • Rivadavia — Mark 7: 12"/50 caliber — Mark 9: 6 × twin turrets • Moreno — Mark 7: 12"/50 caliber — Mark 9: 6 × twin turrets