The dual-purpose radar-controlled single 5-in Gun Mounting Mk 42 was adopted in the late 1950s and early 1960s as the successor to the semiautomatic twin 127-mm (5-in) 38calibre Mk 32 and single 127-mm 54calibre Mk 39 mountings of World War II and the immediate post-war years respectively. The Mk 42 is capable of a much higher rate of fire and is fitted with an automatic ammunition feed system with two 20-round ready-use drums. Driven by electro-hydraulic power units, the Mk 42 can be operated in local or automatic control. Crew for the Mk 42 Mod 7/8 is 14, of whom four are actually on the mount. Over 150 guns of this type are at sea with the US Navy and the navies of Australia, Japan, Spain and West Germany. All bar a few of the US guns have been upgraded to the Mk 42 Mod 10 standard by kit additions, this bringing the mount up to the same equipment fit as the lighter Mk 42 Mod 9 variant which was constructed for the 'Knox' class frigates. This has solid-state electronics, a 10 per cent reduction in power requirements and a crew of only two on the mount, reducing the overall total to 12. The 127-mm gun barrel fitted to the Mk 42 mounts is designated the Mk 18. A semi-active laser-guided projectile is in the procurement stage for these and the later Mk 45 mountings. The round is 1.548 m (5.08 ft) long, weighs 47.4 kg ( 104.5 lb), and is similar in concept to the US Army's Copper head projectile for its 155-mm (6.1-in) howitzers.

Specification Mounting Mk 42 Caliber: 127 mm (5 in) No. of barrels: one
Weights: Mod7/8 65.8 tons, Mod 9 57.65 tons and Mod 10 63.9 tons
Elevation:-5 to +80
Muzzle velocity: 810 m (2, 657 ft) per second
Projectile weight: 31.8 kg (70 Ib)
Maximum rate of fire: 20 rpm
Maximum effective ranges: surface fire 23.8 km ( 14.8 miles), and antiaircraft fire 14.8 km (9.2 miles)

Click here to view MK-42 5-inch/54 Caliber Gun Gallery

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