The project began in with the goal of developing simple light destroyers DDL to support patrol boat operations. The project was rescoped in when the Navy decided to use the ships to replace other destroyers as they retired, leading to an increase in the design's size and complexity. The construction of three DDLs was approved in Concerns over the ships' cost and technological risk led the government to cancel the DDL project in on the RAN's advice, and a variant of the United States' Oliver Hazard Perry -class frigate was procured instead.
During this period, Australian minesweepers and frigates patrolled Malaysia's coastline to counter Indonesian infiltration parties travelling in small craft. These ships also bombarded Indonesian positions in East Kalimantan near the border with Malaysia on several occasions.
The RAN's experiences during this conflict led it to perceive a need for light destroyers and patrol boats tailored to Confrontation-type tasks. When the DDL project began in , the ships' role was to support patrol boats during anti-infiltration operations and complement the Navy's existing destroyer force. The intention was that the DDLs would be fast, simply armed and smaller than conventional destroyers.
The DDL design evolved during the late s. As a result of planning conducted during and , it gradually became clear that the ships would replace rather than complement the Navy's three Daring -class destroyers and four early River-class destroyer escorts. The intended roles for the DDLs' were set in by an agreement between the RAN and Department of Defence , which specified that the ships were to be capable of destroying equivalent surface warships, carrying out maritime interdiction duties, commanding groups of patrol boats and aircraft, have reasonable anti-aircraft and anti-submarine capabilities and be able to provide naval gunfire support to land forces.
The DDL design changed considerably over the life of the project. The initial specification was for a 1,ton escort vessel [ 9 ] and in an early design the class was to have a single 5-inch mm gun as its primary armament and carry a helicopter. These DDLs were to be armed with two five-inch guns and operate a single light helicopter. As an initial stage, Y-ARD was required to develop sketch designs for six different armament configurations using a common hull. These studies found that including an area air defence capability and an ability to operate two helicopters greatly improved the DDL's effectiveness.
