12-inch/45-caliber Mark 5 Naval Gun | |
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![]() Mark 5 gun being hoisted aboard USS Connecticut | |
Type | Naval gun Coastal defence |
Place of origin | United States |
Service history | |
In service | 1906–1930 |
Used by |
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Wars | |
Production history | |
Designer | Bureau of Ordnance |
Designed | 1903[1] |
Manufacturer | U.S. Naval Gun Factory[2] |
Specifications | |
Mass | 53 short tons (48 t) |
Barrel length | 45 ft 0 in (13.72 m) bore (45 calibers) |
Shell | 870 lb (390 kg) |
Caliber | 12 in (305 mm) |
Elevation | -5° to +15° |
Rate of fire | 2–3 rpm |
Muzzle velocity | 2,700 ft/s (820 m/s) |
Effective firing range | 20,000 yd (18,288 m) at 15° elevation 30,000 yd (27,432 m) at 47° elevation As coastal artillery |
The 12-inch/45-caliber Mark 5 gun was an American naval gun that first entered service in 1906. Initially designed for use with the Connecticut-class of pre-dreadnought battleships, the Mark 5 continued in service aboard the first generation of American dreadnoughts.
The 12-inch (305 mm)/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.[1] 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.[2]
The Mark 5 weighed 53 short tons (48 t) and was capable of firing 2 to 3 times a minute. At maximum elevation of 15° it could fire an 870 lb (390 kg) shell approximately 20,000 yd (18,000 m). 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 yd (9,100 m). With an initial muzzle velocity of 2,700 ft/s (820 m/s), the gun had a barrel life of 175 rounds, and was capable of firing either armor-piercing or common projectiles.[1][3]
As designed, the Mark 5 was capable of penetrating 16.6 in (420 mm) of Harvey plated side armor at 6,000 yd (5,500 m), 12.2 in (310 mm) at 9,000 yd (8,200 m), and 9.9 in (250 mm) at 12,000 yd (11,000 m). By comparison the 12-inch/40-caliber Mark 4 it replaced could only penetrate 14.6 in (370 mm), 11.6 in (290 mm), and 9.4 in (240 mm) at those distances, respectively.[1]
During the summer of 1916, Michigan blew out her left hand gun in turret No. 2 during target practice. After an investigation of South Carolina's 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.[1] The lapping heads were later replaced by wire and pisaba brushes.[6][1]
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 yd (27,000 m), 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.[1][7] 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.[4]