hull units converted to become Chieftain, Armoured Vehicle-Launched Bridge Mk.6 (CH AVLB Mk 6). Chieftain Mk.1/2 Upgrade of Chieftain Mk.1 to Chieftain Mk.2 standard, fitted with 650 hp L60 Mk 4A2 engine, training use only Chieftain Mk.1/3 Upgrade of Chieftain Mk.1, fitted with 650 hpL60 Mk 5A engine, training use only Chieftain Mk.1/4 Upgrade of Chieftain Mk.1, fitted with 650 hp L60 Mk 6A engine and improved ranging gun, training use only Chieftain Mk.2 First service model with 650 hp L60 Mk 4A2 engine, L11A2 or L11A3 main gun, NBC system fitted to rear of turret, revised turret stowage, one-piece commander's hatch cover, armour removed from searchlight cover, rigid flotation panels replaced by facility for deep wading, road speed , range , weight , first vehicles issued to 11th Hussars at Hohne in West Germany in early 1967, improved L60 Mk 5A engine fitted 1969 Chieftain Mk.3Improved 650 hp L60 Mk 6A engine with two-stage air cleaner, improved auxiliary generator (Coventry Climax H30 ), better stowage, new No. 15 Mk 2 commander's cupola, road speed improved to , range increased to , weight , 1970 Chieftain Mk 3/2 Fitted with L60 Mk 7A, 1971 Chieftain Mk 3/3 Fitted with 720 hp L60 Mk 7A, Improved main gun range finding, provision for Barr & Stroud TLS (Tank Laser Sight) LF2 laser range finder, With the LF2, the Chieftain became the first vehicle to be fitted with such a range-finding system. 1971 Chieftain Mk 3/G Chieftain Mk.3 with engine induction through fighting compartment. Prototype only Chieftain Mk.3/3P Chieftain Mk 3/3 for Iran, 1973 Chieftain Mk 3/S Production version of Chieftain Mk 3/G with commander's firing control Chieftain Mk.4 Chieftain Mk.3 with increased fuel capacity for Israel Defense Forces (IDF). Only two built. 1973. The Chieftain Mk.4 project was halted at the behest of the British Government due to the perceived adverse effect the sale of Chieftain to Israel was likely to have on the balance of power within the region. Of the two Mk.4 vehicles built, one was scrapped, the other "02 SP 27" was fitted with an NCK Rapier crane and used at Kirkcudbright Training Area Chieftain Mk.5 Final production variant, L60 Mark 8A, with upgrades to the NBC protection system, weight , 1975 Chieftain Mk.5/5P Chieftain Mk.5 for Iran, 1975. Engine later upgraded to L60 Mk 10A, 1977 Chieftain Mk.5/2K Chieftain Mk.5 for Kuwait, 1975 In 1975 all British Army