The Type 3 120 mm 45 caliber naval gun was a Japanese naval artillery and coast defense gun used on destroyers and submarines of the Imperial Japanese Navy during World War I and World War II. It's title properly would be written 12 cm/45 3rd Year Type under the same naming system as the 41 cm/45 3rd Year Type naval gun, 20 cm/50 3rd Year Type naval gun, 15.5 cm/60 3rd Year Type naval gun, 12.7 cm/50 Type 3 naval gun and all other Japanese naval artillery. "Third Year Type" (sometimes written as "Type 3") refers to the Welin breech block used on all these guns. It was an indigenous development of the British-designed QF 4.7 inch Gun Mk I - IV, which had been previously produced in Japanese as the "Type 41", under license from Elswick Ordnance Company, part of Armstrong Whitworth. It should