 Upgraded anti @-@ submarine version for the Royal Navy , based on Australian Mk 50 . More powerful Gnome <unk> @-@ 1 engines , six bladed tail rotor and upgraded avionics ( including new Type 2069 dipping sonar ) , and improved navigation and communications equipment ; 21 new build aircraft plus conversions from <unk> Some were later converted for AEW ( Airborne Early Warning ) duties . 
