O and P-class destroyer

The O and P class was a class of destroyers of the British Royal Navy. Ordered in 1939, they were the first ships in the War Emergency Programme, also known as the 1st and 2nd Emergency Flotilla, respectively. They served as convoy escorts in World War II, and some were later converted to fast second-rate anti-submarine frigates in the 1950s.

Design
The O and P class were based on the hull and machinery of the preceding J class, but with more sheer forward to counter the poor riding qualities of the Js. These ships used the Fuze Keeping Clock HA Fire Control Computer.

O class
The O-class ships were built in two groups of four. The first group had 4.7 in guns. They were in low-angle mounts which could elevate to only 40 degrees, and were additionally fitted with a 4 in anti-aircraft gun in place of one set of torpedo tubes. The second group had 4 in guns in high-angle mounts and were fitted to act as minelayers; they could be recognised by the flat "beaver tail" stern over which the mines were dropped. When carrying mines they had to land Y gun, their torpedo tubes and depth charges. The designed anti-aircraft armament was one quadruple QF 2-pounder "pom pom" and a pair of quadruple 0.5-inch Vickers A/A machine guns. The latter proved to be outdated, and were replaced by 20 mm Oerlikon guns as they became available, with a total of six single mounts eventually being carried.

P class
The P class were repeats of the O class, armed entirely with 4 in guns, in high-angle mounts fitted with a new tall design of shield which did not require the ships to lose a set of torpedo tubes to take on further AA guns.

O class
All ships survived the war. Five of the ships were involved in the Battle of the Barents Sea, Onslow being badly damaged. After the Battle of the Barents Sea, the ships were refitted with tall lattice masts instead of the normal mast.
 * 4.7 inch-armed ships
 * Onslow * (ex-Pakenham), built by John Brown & Company, Clydebank, to Pakistan 1949 as Tippu Sultan, sold out
 * Offa, built by Fairfield Shipbuilding & Engineering Company, Govan, to Pakistan 1949 as Tariq, sold for scrap in 1959
 * Onslaught (ex-Pathfinder), built by Fairfield, to Pakistan 1951 as Tughril, sold out
 * Oribi (ex-Observer), built by Fairfield, to Turkey 1946 as Gayret, sold out
 * 4 inch-armed ships
 * Obdurate †, built by William Denny & Brothers, Dumbarton, sold for scrap in 1964 at J Cashmore's, Newport, Monmouthshire
 * Obedient †, built by Denny, sold for scrap - 1964
 * Opportune †, built by John I. Thornycroft & Company, Woolston, sold for scrap - 1955
 * Orwell †, built by Thornycroft, converted to Type 16 frigate 1952, sold for scrap - 1965

* = flotilla leader

† = fitted for minelaying

P class
They served mainly in the Mediterranean, where four ships were lost.
 * Pakenham * (ex-Onslow), built by Hawthorn Leslie & Company, Hebburn, damaged by gunfire from Italian Navy torpedo boats Cassiopea and Cigno off Marsala 1943-04-16, abandoned and sunk by sister ship HMS Paladin (see Battle of the Cigno Convoy)
 * Paladin, built by John Brown, converted to Type 16 frigate 1954, sold for scrap in 1962
 * Panther, built by Fairfield, bombed and sunk by German aircraft in Scarpanto Strait on 10 September 1943
 * Partridge, built by Fairfield, torpedoed by German Submarine U.565 off Oran, 18 December 1942
 * Pathfinder (ex-Onslaught), built by Hawthorn Leslie, bombed and damaged by Japanese aircraft off Ramtree Island 2 November 1945, never repaired and used as an aircraft target, sold for scrap in 1948
 * Penn, built by Vickers Armstrongs, Walker, sold for scrap - 1949
 * Petard (ex-Persistent), built by Vickers Armstrongs, converted to Type 16 frigate, sold for scrap 1967
 * Porcupine, built by Vickers Armstrongs, torpedoed by German submarine U-602 in Mediterranean 9 December 1942 and broke in two; never repaired and hulked as Pork and Pine, sold for scrap - 1947

* = flotilla leader