20 cm/50 3rd Year Type naval gun

20 cm/50 3rd Year Type naval gun
Tone-class cruiser Chikuma mounted all 4 turrets forward of the bridge.
Type	Naval gun
Place of origin	Japan
Service history
In service	1926 - 1945[1]
Used by	Imperial Japanese Navy
Wars	Second World War
Production history
Manufacturer	Kure Naval Arsenal Muroran Ironworks[2]
Produced	1 GÔ (Mark 1) : 1923 2 GÔ (Mark 2) : 1932
No. built	~300[2]
Specifications
Mass	1 GÔ (Mark 1) : 17.6 tonnes[2] 2 GÔ (Mark 2): 18.7 tonnes
Length	1 GÔ (Mark 1) : 10 metres (33 ft) 2 GÔ (Mark 2) : 10.31 metres (33.8 ft)
Barrel length	1 GÔ (Mark 1) : 9.144 metres (30.00 ft) 2 GÔ (Mark 2) : 10 metres (33 ft)[2]
Shell	1 GÔ (Mark 1) : 110 kilograms (240 lb) 2 GÔ (Mark 2) : 126 kilograms (278 lb)
Calibre	1 GÔ (Mark 1) : 20-centimetre (7.874 in) 2 GÔ (Mark 2) : 8-inch (203.2 mm) [2]
Muzzle velocity	835 m/s (2,740 ft/s)[2]
Maximum firing range	29 kilometres (18 mi)[2]

Third year type 20 cm/50 caliber guns (五十口径三年式二〇糎砲, gojūkōkei sannenshiki ni-maru centi-hō) formed the main battery of Japan's World War II heavy cruisers. These guns were also mounted on two early aircraft carriers, the Kaga and the Akagi before their 1935 reconstruction.^[2] The typical installation was ten 20 cm/50 guns; although Tone-class cruisers carried eight while Furutaka and Aoba-class cruisers carried six. After modernization, Akagi and Kaga carried only six, divided in three casemates per side, after the removal (during the 1935 reconstruction) of the four guns in two turrets on both ships placed on the second deck.

These were built-up guns with an inner A tube, encased by a second tube, encased by a full length jacket. Early guns were partially wire-wound, but later guns dispensed with the wire winding. The guns were breech loaded with two cloth bags of smokeless powder.^[2] Third year type refers to the Welin breech block on this gun. Breech block design began in 1914 AD, the third year of the Taishō period. This breech block design was also used on Japanese 41 cm (16.1 inch), 15.5 cm (6 inch), 14 cm (5.5 inch), 12.7 cm (5 inch), and 12 cm (4.7 inch) naval guns.^[3]