| Ordnance QF 4.5 inch gun Mk I, II, III, IV, V | |
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Mk III guns in BD 'RP10' Mk II mountings on Implacable-class |
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| Type | Naval gun Anti-aircraft gun |
| Place of origin | United Kingdom |
| Service history | |
| Used by | British Commonwealth |
| Wars | Second World War Korean War |
| Production history | |
| Number built | Navy: c. 800 Army: 474 |
| Specifications | |
| Barrel length | Bore: 16 ft 8 in (5.08 m) L/45 (calibres) |
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| Shell | Fixed or Separate QF 55 pounds (24.9 kg) |
| Calibre | 4.45-inch (113 mm) |
| Breech | Mks I - IV: Horizontal sliding block Mk V: Vertical sliding block |
| Rate of fire | 12 RPM for Mk II BD mount. 16 RPM recorded for Mk III UD mount.[1] |
| Muzzle velocity | 2,449 ft/s (746 m/s)[2] |
| Maximum range | 20,750 yd (18,970 m) at 2,449 ft/s (746 m/s). A.A.:41,000 ft (12,000 m)[3] |
The QF 4.5 inch gun has been the standard medium-calibre naval gun used by the Royal Navy as a medium range weapon capable of use against surface, aircraft and shore bombardment targets since 1938. This article covers the early 45-calibre family of guns up to the 1970s. For the later unrelated 55-calibre Royal Navy gun, see 4.5 inch Mark 8 naval gun.
Like all British nominally 4.5 inch naval guns, the QF Mk I has an actual calibre of 4.45 inches (113 mm).[4][5]
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From the BL Mark I gun of 1916 onwards the 4.7-inch (120-mm) calibre was the mid-calibre weapon of choice for the Royal Navy, used particularly on destroyers. Apart from some ships armed with QF 4-inch Mk V guns due to supply problems, it remained the standard weapon for destroyers up to the W class destroyers of 1943. However, its usefulness as an anti-aircraft weapon had been limited by the failure to develop a mounting with elevation over 55°, the lack of a predictive fire control system in destroyer classes built prior to the introduction of the 4.7" twin mount, (see HACS) and the setting of fuzes by hand on early, prewar, mountings. Later 4.7" mountings used mechanical fuze setters that were identical to those used on the 4.5" mountings.[6]
The QF 4.5 inch L/45 was developed originally as a dual-purpose weapon with which to arm aircraft carriers and reconstructed battleships and battlecruisers. It was later developed as a new dual-purpose weapon with which to arm destroyers, supplanting the ubiquitous 4.7 inch gun. Despite the lower calibre, it actually had a heavier shell, resulting in a more powerful weapon.
The nomenclature system for guns used by the Royal Navy can be somewhat confusing. The gun and mounting each have their own Mark number and a letter(s) giving additional information. QF stands for "quick firing", UD for "upper deck", BD for "between decks" and CP for "central pivot".
Some 800 naval 4.5" guns of various marks were built. 474 guns were built for the army, all in 1939-41.
During the 1950s, a change was made in designating the weapons systems which focussed on the gun mount rather than the gun itself. Together with a change from Roman numerals, the Gun QF Mark V on mounting BD Mark VI became simply the Mark 6. The Mark 7 was never produced as the planned Malta class aircraft carriers they would have been used on were never built.
The majority of new escort vessels built for the Royal Navy in the 1950s and 1960s carried at least one Mark 6 mounting, with two in the Leopard class frigate and County class destroyer and three in the Daring class destroyer. This gave these ships a level of firepower unprecedented only 15 years earlier. The Type 81 Tribal class frigates were an exception, using reconditioned Mark V mounts from scrapped C class destroyers that were fitted with RPC and known as the Mark 5* Mod 1.
The evolution of the 45-calibre 4.5 inch gun family ended with the Mark V gun / Mark 6 mounting. It has been replaced by a new weapon of original design, the 4.5 inch Mark 8 with a 55 calibre-long barrel.
Ships with 4.5 inch guns QF Mark I in twin mounting UD Mark III
Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark II
Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark II**
Ships with 4.5 inch guns QF Mark III in twin mounting BD Mark IV
Ships with 4.5 inch guns QF Mark IV in single mounting CP Mark V
Ships with 4.5 inch guns Mark 5* (rebuilt mounting CP Mark V).
Ships with 4.5 inch guns QF Mark V in twin mounting UD Mark VI (later renamed gun Mark 6)
QF Mark II was a single gun mounting (Mounting Mk 1) anti-aircraft gun in static sites. The pedestal mount was bolted to concrete in an unarmoured turret, a travelling platform was available to transport the gun and mounting between positions. The first unit became operational in February 1939. These 16.5 ton anti-aircraft mountings had a max elevation angle of 80 degrees. However, most mountings were Mark 1A with an elevation range of -9.5 to 80 degrees, this enabled the gun to be dual role (AA/CD) in coastal areas, armour piercing was provided for anti-ship engagements.
The guns were fitted with Magslip electrical data transfer from Predictors AA Nos 3, 5 and 10 and were probably used inially with GL radars and UB 10 18 feet base optical height & rangefinders. AA control radars evolved rapidly. The gun was laid and fuzes set by pointer matching, it is unclear the extent to which advances in 3.7-inch fire control were applied to 4.5-inch. However, mid-war Machine Fuze Setter No 10 was added, this improved the rate of fire from 8 to 10 rounds per minute and raised the effective ceiling to 34,500 feet.
Gun positions were usually in the vicinity of naval bases where they could use the naval ammunition supply. However, initially the standard fuze was an igniferous design, No 199 with a maximum running time of 30 seonds that limited performance. Subsequently No 209 a mechanical time fuze was introduced. However, it appears that VT fuzes were not issued.
Guns were usually deployed in troops of 4 as part of a two troop battery, although sections of two guns occupied some positions. Deployment included:
UK (Royal Artillery) June 1940[8]:
(the AA divisions included 3-inch and 3.7-inch regiments in addition to 4.5-inch)
Far East January 1942[9]:
Mediterranean June 1943[10]:
Middle East January 1943[11]:
West Africa Dec 1941[12]:
India Dec 1941[13]:
Colonel Probert of the Armaments Research Department developed rifling with tapered groove depth, and the last few inches of the barrel being smoothebore. This was used with a 4.5 barrel lined down to 3.7 inches, but retaining the large chamber, hence a large propelling charge. Ordnance, QF 3.7 inch Mk 6, only on a static mounting, entered service in 1943 and continued in service until 1959. It had an effective ceiling of 45,000 feet.[14][15]
The high performance of QF 3.7 inch Mk 6 and QF 5.25 inch meant that QF 4.5 inch was not retained in land service after World War II.
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