Persian Gulf. , all ten ships are in service. The RAN intends to start replacing theirs in 2027 when their first Hunter-class frigate is commissioned, while the RNZN ships will remain active until the mid-2030s. Planning and development The Anzac class originated from the RAN's New Surface Combatant (NSC) project, which began in the mid-1980s to find a replacement for the RAN's six River-class destroyer escorts. By 1985, various design briefs ranging from displacement were under consideration, with the RAN emphasising anti-ship missile defence, damage control, and ship survivability based on Royal Navy experiences during the Falklands War. Eventually, the project settled on a ship of approximately displacement. At this time, it was also believed that Australia did not have the capability to design a major warship from scratch, so the decision was made to select a proven foreign design and fit it with an Australian-developed combat system. In early 1986, a review of policy regarding surface combatants saw the NSC classified into the middle of three tiers: a patrol frigate designed to operate on low- to mid-intensity operations in Australia's Economic Exclusion Zone. Around the same time, the need to replace the RNZN's Leander-class frigate force with new warships was under consideration. The government saw maintaining a blue-water capable force built around three or four frigates as important, but the cost of acquiring and maintaining such a force was prohibitive, once it became clear on the basis of RN & RAN studies that the generally favored Type 21 design, lacked the space and volume for the required range & development, and a joint Anzac project offered the RNZN the first chance in 20 years, something like new deepwater warships. The NZ 1983 Defence Review on the basis of RN theoretical study and enthusiasm for the 2400 Vicker sub-project, saw a submarine force as the only way of maintaining an RNZN as a combat force, and the Muldoon government actually entered into a memo of understanding with Australia for the joint development of what became the Collins submarines and assigned staff to the Australian project, however, it became clear that surface vessels were also required and the cost risk was too high. Alternate suggestions, such as reducing the RNZN to a coast guard-type force responsible for coastal and fisheries protection, replacing the frigates with smaller offshore patrol vessels, or reorienting the navy to primarily operate submarines, were made in several