At the same time, the U.S. Navy was still operating anti-submarine air patrols with P5M/SP-5B Marlin seaplanes from NAS Bermuda at the West End. Whereas the Second World War air patrols had protected merchant shipping in the Atlantic, the Cold War patrols aimed to guard US cities from Soviet submarines armed with ballistic missiles with nuclear warheads. The Martin flying boats the Navy had used since the 1950s were withdrawn and replaced by landplanes.