08/31/2014. Remarks by Johan Visschedijk: "When the Short 184 failed to repeat its first operational success as a torpedoplane, due mainly to insufficient power in reserve to cope with both a torpedo and ample fuel, particularly in hot weather, Captain Murray F. Sueter (Director of the Admiralty's Naval Air Department) and Flight Lieutenant Douglas H. Hyde-Thomson, both leading figures in the development of torpedo dropping, realized that they would have to face the complication of twin engines or wait for a power unit giving at least 300 hp, preferably at a weight no greater than that of current 200 hp engines. Early experience with the Wight twin-fuselage torpedo seaplane had provided only double trouble with no advantage in performance, plus an unnecessarily large aircraft for the task.
Nevertheless, a twin-engined prototype torpedo-seaplane with 225 hp Sunbeam engines was ordered from the Blackburn Aeroplane Co. and Louis H. Coatalen, Sunbeam's Chief Designer, was urged to press on with the development of a 300 hp engine in competition with the rapidly improving Rolls-Royce Eagle; all supplies of the latter were already earmarked for bombers (Airco D.H.4 and Handley Page O/100) and for Curtiss and Porte flying boats which had begun to prove their ability to fight off and destroy Zeppelins at long-range. The Admiralty's objectives of torpedoing the German and Austrian fleets in their respective anchorages at Wilhelmshaven and Pola had to yield priority to the urgent needs of the Western Front and North Sea battles, and consequently no Rolls-Royce Eagles could be spared for float seaplanes in 1916.
Meanwhile, Horace and Oswald Short prepared two designs based on the new Sunbeam engine; the first was a cleaned-up and strengthened torpedo-seaplane of almost the same size as the Mann Egerton Type B, with a roomier fuselage, increased chord and gap and similar wing arrangement; the second was a patrol seaplane with the same fuselage and chassis as the first, but having equal-span three-bay wings analogous to Type 184. Two prototypes of each were ordered as a batch of four, the torpedoplanes (Type 310-A) being c/n S.299-S.300 (serials 8317-8318) and the patrol seaplanes (Type 310-B) being c/n S.311-S.312 (serials 8319-8320); the latter were alternatively known as 'North Sea Scouts'.
The Sunbeam engine, later named Cossack, was rated at 310 hp (normal) and 320 hp (maximum), but in production batches the normal rating was soon raised to 320 hp, hence series aircraft were referred to as the type 320. Maximum priority was accorded to the torpedo version, once the engines were available, with a view to putting them to use in the Adriatic as soon as possible. General design features were similar to the 184's, but the 18 in (46 cm) Mark IX torpedo, weighing 1,000 lb (454 kg) against the 810 lb (367 kg) of the 14 in (36 cm) Whitehead, was carried close under the belly of the fuselage. The rear cross-strut of the float chassis was made detachable to permit a clear passage when the torpedo was launched, and extra struts were provided to secure the inner faces of the floats while the cross-strut was removed.
The engine installation was generally similar to that of the 260 hp Sunbeam in the 184, with the same block radiator above and an auxiliary radiator and oil cooler on the port side of the fuselage between the wings; in later production batches the main radiator was enlarged and the auxiliary unit deleted. At first the central exhaust manifold had a down-swept stack, but this resulted in fumes in the cockpit and only after various vertical and lateral pipes had been tried was the final stack, upswept and canted to port, found satisfactory; for a time the prototypes had a parallel pair of pipes close together. The prototypes had four-bladed airscrews, but two-bladers were standard on production aircraft.
The pilot occupied the rear cockpit, to obviate the need for ballast under a variety of loading conditions, and the front cockpit provided all the normal stowages and equipment for the observer; in later batches there was also a Scarff ring mounted on struts level with the upper-wing trailing edge, which gave the observer a clear field of fire for a Lewis gun, but was a position of great exposure for which no alternative could be found; however, the observer could not be carried at the same time as a torpedo.
The first prototype was ready for flight at Rochester in July 1916, and the second in August, both being first flown by Ronald Kemp. After acceptance, the two prototypes were urgently dispatched to the RNAS seaplane base at Otranto, where it was intended to station twelve of the type, but during early torpedo trials both seaplanes broke up in the air. At first it was thought that the rebound from suddenly releasing so great a weight might have been responsible for structural failure, but the defect was traced to the rear float attachment; this was redesigned with modified floats pitched farther apart and extra struts bracing the floats to the lower wings; the extra float struts were V-shaped welded tube assemblies which swung down when released for wing folding; a notice prominently painted on both sides of the fuselage read: 'Very Important: The Removable Rear Crossbar Must always be in Position Before the Wings are Folded'; in this form the aircraft was designated the 310-A4.
The second 310-B (c/n S.312) was converted during construction into an additional 320 in February 1917 and renumbered N1480. Series production had already begun at Rochester with a batch of thirty (S.354-S.363, N1150-N1159, and S.334-S.353, N1300-N1319) for urgent delivery to RNAS Otranto, Italy and RNAS Kalafrana, Malta, to be followed by batches of 24 (S.365-S.388, N1481-N1504) and twenty (S.399-S.418, N1390-N1409). Concurrently a contract was placed with Sunbeam for batches of thirty (N1360-N1389) and twenty (N1690-N1709) respectively; it seems that the final batches from Short Bros and Sunbeam were exchanged, probably to ease temporary supply difficulties. No later production was undertaken because official policy had changed in favor of deck-landing torpedoplanes, following successful trials after the second refit of HMS Furious.
On its first operation the 320 was robbed of success by a sudden gale which wrecked all six of those detailed for a torpedo attack on the night of September 3, 1917, against a flotilla of enemy submarines off Cattaro in the Adriatic. To conserve fuel, they were towed on rafts to Traste Bay, where they arrived successfully but were capsized by a sudden storm at 4 am, just at zero hour for take off; so the opportunity passed, and no other chance presented itself within the capability of the aircraft for several months. Then, in January 1918, the German cruiser Goeben made a bolt for freedom hrough the Dardanelies but ran aground at Nagara Burnu; while stuck fast, she was repeatedly bombed without effect by the RNAS, and two 320s, with torpedoes, were hastily embarked on Manxman, but arrived too late to join in the attack, for after a week the Goeben's crew refloated her and she escaped to shelter in the Bosphorus.
To improve experience of torpedo launching, a series of trials were run at Calshot in February 1918, in which forty torpedoes were launched by four 320s; only three weapons were lost, and the lessons learned were put to use at the Torpedo School at Kalafrana, Malta. The majority of the 320s in service were used in the long-range patrol role, when they had an endurance of six hours while carrying a crew of two and two 230 lb (104 kg) bombs.
No submarine kill by a 320 was ever confirmed, although a probable was scored by one from Kalafrana on a U-boat which attacked a French battleship off Malta on February 8, 1918. The total number of 320s built was 127, of which fifty remained in service with the RAF at the Arrnistice; N1404 and N1409 were in use at Grain for experimental work in June 1918, and six, believed to be c/n S.370-S.375 (N1485-N1490), were supplied to the Imperial Japanese Navy for training and trials at the end of 1917.
The 310-B, completed in September 1916, was not adopted for production, being not a sufficient improvement on the 184. Possibly if all the torpedo-seaplanes had been needed in their original role there would have been some justification for a structurally similar long-range Scout, but, with no niche to fill, the prototype S.311 (8319) was used in April 1917 only for air-firing trials at Grain of a 6-pounder Davis recoilless gun, arranged to fire upwards and forwards as an anti-Zeppelin weapon.
It was mounted on a trammel across the rear cockpit, which also had a Lewis gun for self-defense; the pilot was in front as in the 184, which the 310-B closely resembled in layout, although it was bigger all round and its deeper fuselage gave better protection to the crew. For some reason, no doubt to improve the pilot's view ahead as well as to avoid muzzle blast damage from the Davis gun, the top center section was left open and the radiator was separated laterally into two parallel blocks, with a clear space in the middle. The gun was a later model of that tested at Great Yarmouth in 1915 on Short pusher S.81 (126), but was still a single-shot type incapable of being reloaded in the air; in any case it could only be aimed at an angle to the flight path, so it was quite unsuitable for aerial use, even when directed downwards as an anti-submarine weapon."
