Demolisher
The biggest change came with the weaponry. The trusty 230mm Petard mortar was replaced with the new Ordnance BL 6.5″ Mk.I. This 165mm bore demolition gun was a breach loader, a vast improvement over the Petard. The gun fired a 64 lb (29 kg) High Explosive Squash Head (HESH) shell up to 2,400 m (2,600 yd). Thirty-one rounds of ammunition were carried in the tank. The gun was initially tested against various sizes of concrete blocks, and oil barrels filled with concrete. It succeeded in pulverizing almost all of these targets. The gun was reportedly accurate enough to blast a bridge girder at 600 yards (549 meters), or hit a pillbox or bunker at 1400 yards (1280 meters). At greater ranges, it was an effective Area-Of-Effect (AOE) weapon. This was a huge range increase compared to the 100 yards (91 meters) range of the Petard. The round had no shell case in the traditional sense. Instead, the charge was placed inside a perforated base connected directly to the warhead that remained attached in flight.
Sources:FV3903 Churchill AVRE - Tank Encyclopedia