Master SM-350-036 HMS Repulse armament - 15in (6pcs), 4in QF (6pcs), 4in BL (9pcs) barrels

The BL 4-inch Mk IX naval gun is a 102 mm caliber naval gun from the interwar period and both world wars. The gun was developed at the beginning of World War I and entered service with the Royal Navy in 1916. The total weight of the gun was about 2 tons, and its barrel was 45 calibers, or 4.572 meters long. The maximum rate of fire of this gun was 10-12 rounds per minute, and the initial velocity of the shells was around 800 m / s. In turn, the maximum range was about 12,500 meters. The gun was structurally based on two cannons: the QF 4 inch Mk V gun (from which it took the barrel) and the BL 4-inch Mark VIII naval gun (from which it took the bolt). It was originally developed as an additional armament for Renown-class and Glorious / Courageous-class battleships. Its main goal was to combat light enemy surface units, and in its design, particular emphasis was placed on achieving the highest possible rate of fire. However, during World War II, it was used primarily on Flower-class corvettes and mines.