The G- and H-class destroyers were a group of 18 destroyers built for the Royal Navy during the 1930s. Six additional ships being built for the Brazilian Navy when World War II began in 1939 were purchased by the British and named the Havant class. The design was a major export success with other ships built for the Argentine and Royal Hellenic Navies. They were assigned to the Mediterranean Fleet upon completion and enforced the Non-Intervention Agreement during the Spanish Civil War of 1936–1939.

Most ships were recalled home or were sent to the North Atlantic from October to November 1939, after it became clear that Fascist Italy was not going to intervene in World War II. Then they began to escort convoys and patrol for German submarines and commerce raiders. Two ships were lost to German mines in the first six months of the war. Three more were lost during the Norwegian Campaign, one in combat with a German cruiser and two during the First Battle of Narvik in April 1940. The Battle of France was the next test for the destroyers from May to June, with many of the Gs and Havants participating in the evacuation of Dunkirk and the subsequent evacuations of Allied troops from western France. Three ships were sunk, two by bombs and the other by torpedoes. Most of the H-class ships were sent to the Mediterranean in May in case Mussolini decided to attack France and the majority of the surviving Gs were sent to Force H at Gibraltar in July. Two of them, and , participated in the Battle of Dakar, before being assigned to the Mediterranean Fleet with their sister ships. By the end of the year, the ships participated in several battles with the Royal Italian Navy, losing two to Italian mines and torpedoes, while sinking two Italian submarines. The Havants spent most of the war in the North Atlantic on convoy escort duties, losing half their number to German submarines, while helping to sink six in exchange by the end of the war.

The G- and H-class ships of the Mediterranean Fleet escorted numerous Malta convoys, participated in the Battle of Cape Matapan in March 1941 and covered the evacuation of troops from Greece and Crete from May to June, losing two to German bombers and another so badly damaged that she was later written off. By the end of the year, they had sunk three submarines, two Italian and one German. Three Hs participated in the Second Battle of Sirte in March 1942, during which one was damaged. Further damaged by aerial attacks, she was ordered to Gibraltar and ran aground in transit and had to be destroyed. Another was torpedoed and lost during Operation Vigorous in June. The ships sank two more submarines during 1942 and three destroyers began conversion to escort destroyers late that year and early in 1943. Two of the four surviving Gs and Hs were transferred to the Royal Canadian Navy (RCN) while under conversion. All of the surviving ships joined their Havant half-sisters on escort duty in the North Atlantic in 1943.

One ship was sent to the Mediterranean in 1944 while three others were transferred to the UK in preparation for Operation Overlord. Between them they sank five German submarines in 1944 with another in 1945. Worn-out and obsolete, the survivors were either broken up for scrap or sold off after the war.

Design and description (G and H classes) The G class were ordered as part of the 1933 Naval Construction Programme, the H class following in 1934. These ships were based on the preceding F class, but the elimination of cruising turbines and the development of more compact machinery allowed their dimensions and displacement to be slightly reduced. The H class were repeats of the G's with some minor differences. All of the destroyers were fitted with ASDIC (sonar) and the ability to use the Two-Speed Destroyer Sweep (TSDS) minesweeping gear.English, pp. 75, 88, 102

The G- and H-class destroyers displaced at standard load and at deep load. The ships had an overall length of , a beam of and a draught of .Lenton, pp. 159–160 Their peacetime complement was 137 officers and ratings, which was intended to increase to 146 in wartime. The ships were at their stability limit as built and the Director of Naval Construction believed that no additions in top weight should be made without an equal amount of weight being removed.English, pp. 89–90

They were powered by two Parsons geared steam turbines, each driving one propeller shaft, using steam provided by three Admiralty 3-drum boilers that operated at a pressure of and a temperature of . was fitted with one Johnson boiler in her aft boiler room. The turbines developed a total of and gave a maximum speed of . The destroyers carried a maximum of of fuel oil that gave them a range of at .

All of the ships had the same main armament, four quick-firing (QF) Mark IX guns in single mounts, designated 'A', 'B', 'X', and 'Y' from front to rear. The guns had a maximum elevation of 40°; the G class achieved this with a lowered section of the deck around the mount, the "well", that allowed the breech of the gun to be lowered below deck height, but the new gun mount used in the H class was designed to reach that elevation without the necessity for the clumsy "wells".Whitley, pp. 109–110 They fired a shell at a muzzle velocity of to a range of .Campbell 1985, p. 48 served as the testbed for the twin 4.7-inch gun mount used for the and the J, K and N classes that temporarily replaced 'B' gun. For anti-aircraft (AA) defence, they had two quadruple mounts for the QF 0.5-inch Vickers Mk III machine gun on platforms between the funnels. The G- and H-class ships were fitted with two quadruple mounts for 21-inch (533 mm) torpedo tubes, although trialled the new quintuple mount. The ships were also equipped with two throwers and one rack for 20 depth charges.Lenton, pp. 159–161

The main guns were controlled by an Admiralty Fire Control Clock Mk I that used data derived from the manually operated director-control tower and the separate rangefinder situated above the bridge. They had no capability for anti-aircraft fire and the anti-aircraft guns were aimed solely by eye.Campbell 1985, pp. 14–15; Hodges & Friedman, pp. 12, 17 and Hereward saw the introduction of a new style of bridge that would become standard on all Royal Navy fleet destroyers from the through to the of 1944. This was necessary as Hereward was fitted with a prototype twin-gun mounting that had a trunnion height higher than the previous weapons, therefore it was necessary to raise the wheelhouse to allow the helmsman to see over the top. Raising the wheelhouse meant it had to be placed in front of, rather than underneath, the bridge, and it was given angled sides, resulting in a characteristic wedge shape with a sloping roof.Friedman, p. 224

Wartime modifications Beginning in May 1940, the after bank of torpedo tubes was removed and replaced with a QF 12-pounder Mk V anti-aircraft gun, the after mast and funnel being cut down to improve the gun's field of fire. Four to eight QF 20 mm Oerlikon cannons were added to the surviving ships, usually replacing the .50-calibre machine gun mounts between the funnels. One pair of these was added to the bridge wings and the other pair was mounted abreast the searchlight platform. Early in the war, depth charge stowage increased to 44.Friedman, pp. 236–237 By 1943, only four ships were still afloat and all had the 'Y' gun on the quarterdeck removed to allow for additional depth charge stowage and two additional depth charge throwers. The 12-pounder was removed to allow for the installation of a Huff-Duff radio direction finder on a short mainmast and for more depth charges. All of the survivors, except , had 'A' or 'B' gun replaced by a Hedgehog anti-submarine spigot mortar, and their director-control tower and rangefinder above the bridge removed in exchange for a Type 271 target-indication radar. 'A' gun was later replaced in while Hero had exchanged 'B' gun for a Hedgehog and a twin-gun mount for QF six-pounder Hotchkiss guns for use against U-boats at very close range. A Type 286 short-range, surface-search radar, adapted from the Royal Air Force's ASV radar, was also added. The early models, however, could only scan directly forward and had to be aimed by turning the entire ship.

Flotilla leaders

As per the E and F class, the flotilla leaders were built to an enlarged design, incorporating a fifth 4.7-inch gun in 'Q' position, between the funnels and were based on the F-class leader, .Whitley, p. 107 Grenville was shorter and heavier than Hardy as she used compact Yarrow-type side fired boilers while Hardy was slightly beamier. They displaced at standard load and at deep load. The ships had an overall length of , a beam of Friedman, pp. 224, 299 and a draught of . The ships carried a total of 175 personnel which included the staff of the Captain (D), commanding officer of the flotilla.Whitley, pp. 97, 107 Their turbines were more powerful than the private ships, which made them faster; their propulsion machinery was otherwise identical. Both ships were early wartime losses and consequently received no modifications.

Havant class The Havants were laid down in 1938 for Brazil and requisitioned on 5 September 1939. They were optimized for anti-submarine work and were completed without 'Y' gun and were equipped with eight throwers and three racks for a total of 110 depth charges. Unlike their half-sisters, they were fitted with a combined rangefinder-director above the bridge. Wartime modifications were similar to the other G- and H-class ships as a 12-pounder AA gun replaced the aft torpedo tubes, 20 mm Oerlikons were added on the bridge wings and a Type 286 radar was installed. Later modifications replaced the .50-calibre machine guns with a pair of Oerlikons, a Type 271 radar was added that replaced the rangefinder-director, a Hedgehog was substituted for 'A' gun, the 12-pounder removed for more depth charge stowage, and a HF/DF mast was installed aft.Lenton, p. 163

Ships Royal Navy G class

+ Construction dataShipBuilder English, p. 90Laid downLaunchedCompleted FateAlexander Stephen and Sons, Linthouse15 September 1934 26 September 1935 25 February 1936 Wrecked by German bombers, declared a constructive total loss, 20 January 1941 Fairfield Shipbuilding & Engineering Company, Govan22 August 1934 24 October 1935 3 March 1936Sold to the Royal Dutch Navy, 14 November 1947 and converted into a training ship, scrapped, 19644 September 19347 November 193522 February 1936Sunk by a mine, 21 November 1939English, p. 95John I. Thornycroft & Company, Woolston 15 August 193422 July 193522 January 1936Sunk by the German heavy cruiser , 8 April 1940English, p. 9730 August 1934 18 September 1935 20 March 1936Sunk by the , 29 May 1940English, p. 98Alexander Stephen and Sons, Linthouse3 October 193412 November 193528 March 1936Sunk by German aircraft, 29 May 1940English, p. 99(Flotilla leader)Yarrow & Company, Scotstoun29 September 1934 15 August 19351 July 1936 Sunk by a mine, 19 January 1940Vickers Armstrongs, Barrow-in-Furness20 September 19341 February 1936Sunk by German aircraft, 22 May 1941English, p. 1006 March 1936Transferred to the RCN, 1 March 1943; scrapped, August 1946English, p. 101

H class