The Attack class was ordered in 1964 to operate in Australian waters as patrol boats (based on lessons learned through using the Ton-classminesweepers on patrols of Borneo during the Indonesia-Malaysia Confrontation, and to replace a variety of old patrol, search-and-rescue, and general-purpose craft.[1] Initially, nine were ordered for the RAN, with another five for Papua New Guinea's Australian-run coastal security force, although another six ships were ordered to bring the class to twenty vessels.[1] The patrol boats had a displacement of 100 tons at standard load and 146 tons at full load, were 107.6 feet (32.8 m) in length overall, had a beam of 20 feet (6.1 m), and draughts of 6.4 feet (2.0 m) at standard load, and 7.3 feet (2.2 m) at full load.[2][1] Propulsion machinery consisted of two 16-cylinder Paxman YJCM diesel engines, which supplied 3,460 shaft horsepower (2,580 kW) to the two propellers.[2][1] The vessels could achieve a top speed of 24 knots (44 km/h; 28 mph), and had a range of 1,200 nautical miles (2,200 km; 1,400 mi) at 13 knots (24 km/h; 15 mph).[2][1] The ship's company consisted of three officers and sixteen sailors.[2] Main armament was a bow-mounted Bofors 40 mm gun, supplemented by two .50-calibre M2 Browning machine guns and various small arms.[2][1] The ships were designed with as many commercial components as possible: the Attacks were to operate in remote regions of Australia and New Guinea, and a town's hardware store would be more accessible than home base in a mechanical emergency.[3]