standard fuze was an igniferous design, No 199 with a maximum running time of 30 seconds that limited performance. Subsequently, No 209 a mechanical time fuze was introduced. 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: 1st AA Division - 48 2nd AA Division - 40 3rd AA Division - 64 4th AA Division - 52 5th AA Division - 24 6th AA Division - 52 7th AA Division - 64 (the AA divisions included 3-inch and 3.7-inch regiments in addition to 4.5-inch) Far East January 1942: Singapore - 4 (Hong Kong & Singapore Artillery) Mediterranean June 1943: Malta - 10 Middle East January 1943: Aden - 2 (Hong Kong & Singapore Artillery) Port Said - 2 (Royal Malta Artillery) West Africa Dec 1941: Takoradi - 6 India Dec 1941: Bombay - 6 Colonel Probert of the Armaments Research Department developed rifling with tapered groove depth and with the last few inches of the barrel being smoothbore. This was used with a 4.5 barrel lined down to 3.7 inches but retaining the large chamber, allowing a large propelling charge to be employed. 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. 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. Surviving examples Australia Twin Mk V/Mk 6 turrets on museum ship at Australian National Maritime Museum, Sydney, Australia. Twin Mk V/M6 6 turret from on Spectacle Island, Sydney, Australia. Twin Mk V/Mk 6 turret from HMAS Stuart on display at HMAS Stirling, Garden Island (Western Australia). Twin Mk V/Mk 6 turret from HMAS Derwent at Rockingham Naval Memorial Park, Rockingham, Western Australia. Twin Mk V/Mk 6 turret from HMAS Swan at Princess Royal Fortress, Albany, Western Australia. This turret is open and accessible to visitors. Twin Mk V/Mk 6 turret from HMAS Torrens at Princess Royal Fortress, Albany, Western Australia. Twin Mk V/Mk 6 turret used as a static training aid outside the Gunnery School, HMAS Cerberus, Crib Point, Australia. Twin Mk V/Mk 6 turret as a gate guardian at the West