The program was started by Admiral Arleigh Burke as a response to estimates that the Soviets would have a force of about 300 modern fast-attack submarines by 1957. The US Navy was unable to produce enough destroyer escorts (frigates after 1975) and other anti-submarine warfare-capable ships to counter this threat, given other priorities such as new anti-aircraft warfare-capable frigates (cruisers after 1975) and aircraft carriers, so Burke instead looked for ways to modify the existing World War II-era destroyer fleet, which was rapidly becoming outdated anyway.