but with the exception of , they were all eventually upgraded to the twin mount. For underwater targets, it was equipped with a Hedgehog anti-submarine mortar with depth charge rails and four side-mounted throwers aft for a 10-charge pattern (some had 8 throwers for a 14-charge pattern for a brief period until this was abandoned). River-class frigates were the first Royal Canadian Navy warships to carry the 147B Sword horizontal fan-beam active sonar transmitter, in addition to the regular ASDIC. This allowed the ship to maintain contact with targets even while firing, unless a target was struck. Better radar and radio direction-finding equipment improved the RCN's ability to find and track enemy submarines over previous classes. The River-class design was used as the basis for the United States Navy's (which served in the Royal Navy as the ); the hull design was later elaborated into the and subsequently the . Ships in class Two hundred and forty-three frigates were built in Britain, Canada and Australia for seven navies during World War II. Vessels lost in action Survivors On display in Brisbane, Australia is , the last complete River-class frigate, preserved at the Queensland Maritime Museum. served as a convoy escort during the Battle of the Atlantic and was present at the D-Day landings. In 1947, Greek shipowner Aristotle Onassis purchased her for scrap value and converted her into a luxurious superyacht named Christina O, after his daughter. The vessel is now owned by John Paul Nicolaou, who lets the yacht for elite charters and cruises. , formerly served as a convoy escort during World War II and later transferred to the Israeli Navy and then the Royal Ceylon Navy, which later became the Sri Lankan Navy. She was withdrawn from active duty in 1980 and is now used as a training ship by Sri Lanka. , formerly , is preserved in Seikkyi, Myanmar. In fiction "HMS Saltash" was a fictional River class frigate in Nicholas Monsarrat's 1951 book The Cruel Sea. (In the 1953 Jack Hawkins film version she is called "HMS Saltash Castle", and was played by the corvette .) played the fictional frigate "HMS Rockhampton" in the 1955 John Wayne film The Sea Chase. (She had just been recommissioned as a Prestonian class upgrade of the Canadian River-class frigate, after ten years in reserve.) "HMS Nairn" was a fictional River-class frigate in Alistair MacLean's 1955 book HMS Ulysses.