The Curtiss H-12 ‘Large America’ was a larger development of the Curtiss H-4 that was developed in response to RNAS experience with the H-4, and that served with the US Navy and RNAS.
The Curtiss H-4 was very similar to the earlier H-1 ‘America’, which when it was first built was the largest flying boat yet constructed. The H-1 had been developed just before the outbreak of the First World War for an attempt to fly across the Atlantic. It had originally been designed as a twin engine pusher biplane, with an enclosed cockpit to give the crew shelter during the long voyage. Early in 1914 the project was joined by John Porte, a former officer in the Royal Navy who had been invalided out in 1911 and then become interested in flying boats. He would have been the pilot for the trans-Atlantic flight, but it was cancelled after the outbreak of war. Porte then returned to the Navy, and was given command of the Naval Air Station at Felixstowe. He convinced the Admiralty to purchase the two H-1 ‘Americans’, and to place orders for the very similar Curtiss H-4 (later known as the ‘Small America’. The first H-4s arrived early in 1915, but they didn’t live up to expectations. They were fine once in the air, but performed poorly on the water, and struggled to take off with a full load. Porte began a series of experiments, combining the wings of the H-4 with his own experiment hulls. This eventually resulted in the sole Felixstowe F.1, the start of a line of British improvements on the Curtiss original.
The H-4 was followed by a slightly mysterious aircraft, referred to in British wartime sources as the Curtiss H.8. One prototype of this design, serial number 8650, was delivered to Felixstowe in March 1916. Photographs of this aircraft show a different design to Curtiss’s own H-8 (another rather obscure design). The prototype was delivered with two 160hp Curtiss engines, but these weren’t powerful enough for it to take off when carrying a full military load! It was given two 250hp Rolls-Royce engines, and was then able to take off, although still performed badly on the water. In an attempt to fix the problems, Porte produced a new hull based on his Felixstowe F.1, and combined it with the flight surfaces of the 8650, to produce the sole Felixstowe F.2. This was followed into production by the similar F.2A. At the same time the Admiralty modified their existing order for fify H-8s into one for the larger H-12.
The prototype of the Curtiss H-12 (Model 6A) was developed in the autumn of 1916. It was larger, and with more powerful engines than the H-4. It was an unequal span, three-bay biplane, originally powered by two 160hp Curtis V-X-X engines carried between the wings, and driving tractor propellers. It had two cockpits – one amidships and one in the nose, with the pilots side by side in the nose and the observer and gunner in the amidships cockpit. The hull was constructed from laminated wood with a veneer finish. The H-12 had a similar planing bottom to the H-4, with a shallow ‘V’ and a concave curve to the hull between the keel and the edge of the sponsons. It had thicker sponsons which increased its buoyancy towards the bows.
The pilot’s position was protected by a large curved windscreen, with a glazed roof section. Some versions were armed, with twin machine gun mountings in the amidships cockpit and the nose, and it could carry bombs below the nose. The H-12 performed well on the water and in the air, but both of its main users soon found that it was badly under powered.
A total of 84 H-12s were purchased by Britain, where they were known as the ‘Large America’, to distinguish them from the H-4 ‘Small America’. The H-12 was used on anti-submarine patrols in the waters around Britain and Ireland in 1916-17, with the first aircraft emerging late in 1916. The H-12 entered service before the Felixstowe F.2A, which didn’t reach combat units until February 1918.
The first batch of H-12s replaced an order for fifty H-8s. The sole H-8 (serial number 8650) was developed into the sole Felixstowe F.2, and the remaining forty nine aircraft (8651-8699) as the H-12. Another batch of fifteen H-12s were ordered and allocated the serial numbers N1160-N1174, but these aircraft were delivered as the H-16, with the serial numbers N4060-N4074.
The original engines were soon replaced with 275hp Rolls-Royce Eagle I engines, becoming the H-12A, then with the 375hp Rolls-Royce Eagle VIII, becoming the H-12B. The H-12 also suffered problems with their laminated wood hulls. As a result Lieutenant John Porte of the RNAS, who had played a part in the design of the original H-1 ‘America’, began work on a new hull. This was combined with the Curtiss wings and tail and Rolls Royce engines to produce the Felixstowe flying boats, starting with the F.1. In an unusual twist, the last version of this British update, the Felixstowe F.5, later entered production in the United States, where it was generally known as the Curtiss F-5L.
Some of the British H-12s were given the hull and tail of the Felixstowe F.2A, becoming the H.12 Convert.
The US Navy ordered twenty H-12s, this time powered by two 200hp Curtiss V-2-3 engine. The US Navy also found their boats underpowered, and replaced the Curtiss engines with 360hp Liberty engines, when they were designated as the H-12L. The US aircraft remained in service until 1920, when they were scrapped and their role taken over by the improved H-16.
The H-12 was used on the ‘Spider Web’ patrols, an attempt to catch any U-boats that crossed an area of the southern North Sea between Felixstowe and the Hook of Holland, centred on the North Hinder Light Vessel. On 20 May 1917 H-12 no.8663 attacked a U-boat just to the north-east of the light vessel. This appears to have been UC 36, and the attack is often said to have sunk the submarine, making it the first U-boat sunk by aircraft of the RNAS. However it is also possible that UC 36 survived this attack, only to be rammed and sunk by a French merchant ship on the following day. The aircraft itself was badly damaged when it landed in a heavy swell after returning from this patrol, and had to be written off. The first confirmed victory was probably thus the sinking of U-66 by H-12 no.8656 near the Isles of Scilly on 27 May 1917. This sinking has been verified by the discovery of the wreck of a U-boat in the right location. Many other attacks were carried out, and at the time several victories were allocated to the flying boats, although most of the boats concerned are now believed to have been sunk by other causes (in particular minefields) – presumably because attacks that caused clear damage were assumed to have resulted in a sinking, which was then allocated to a U-boat that was known to have been lost. Even so the constant air patrols made it much more tiring for the U-boat crews to reach their patrol areas.
The H-12 was used against Zeppelins. On 14 May 1917 H-12 no.866 was sent to attack Zeppelin L 22, which had been reported near the Terschelling Light Vessel. The flying boat was sent out to the light vessel, and soon sighted the zeppelin. The H-12 was armed with Brock and Pomeroy ammo, and successfully shot the Zeppelin down not far off Texel. On 14 June 1917 H-12 no.8677 shot down L 43 using a mix of tracer, ball and Brock and Pomeroy ammo. After this the Zeppelins tended to fly at higher altitudes, which put them above the effective operating height of the flying boats, but also made them less effective.
On 20 July 1918 RAF Killingholme became an US Naval Air Station. At least four H.12Bs were transferred from British to American control for service at the new base, along with five F.2As and two H.16s.
Engine: Two Rolls Royce Eagle I inline piston engines
Power: 275hp each
Span: 92ft 8 1/2in
Length: 46ft 6in
Height: 16ft 6in
Empty equipped weight: 7,293lb
Maximum take-off weight: 10,650lb
Max speed: 85mph
Service ceiling: 10,800ft
Endurance: 6 hours
Armament: Four .303in Lewis machine guns in two twin mounts, one in bow, one amidships
Bomb load: 460bl bombs under wings