Soon after the Centurion's introduction, Royal Ordnance finished work on the 84 mm calibre Ordnance QF 20 pounder tank gun. By this point, the usefulness of the 20 mm Polsten had been called into question, it being unnecessarily large for use against troops, so it was replaced with a Besa machine gun in a completely cast turret. The new Centurion Mark III also featured a fully automatic stabilisation system for the gun, allowing it to fire accurately while on the move, dramatically improving battlefield performance. Production of the Mk 3 began in 1948. The Mk 3 was so much more powerful than the Mk 1 and Mk 2, that the earlier designs were removed from service as soon as new Mk 3s arrived, and the older tanks were then either converted into the Centurion armoured recovery vehicle (ARV) Mark 1 for use by the Royal Electrical and Mechanical Engineers or upgraded to Mk 3 standards. Improvements introduced with the Mk 3 included a more powerful version of the engine and a new gun sight and gun stabiliser.