In 1919 the Royal Navy had an urgent need for a three-seat spotter/reconnaissance aircraft. In order to save money, it was decided to adapt the existing Airco DH.9A, for which part completed airframes were available in large numbers following the end of the First World War and the subsequent cancellation of production orders. The initial attempt was carried out by Armstrong Whitworth Aircraft, adding provision for an observer and removing the stagger from the wings to produce the Armstrong Whitworth Tadpole.
Further development, however, was passed on to Westland, who further modified the aircraft to produce the Walrus, with a 450 hp (336 kW) Napier Lion II engine replacing the Liberty engine of the DH.9A and Tadpole. Like the DH.9A, the Walrus was a single-engined, two-bay biplane. It was fitted with an extra cockpit for the observer/radio operator behind the gunner’s cockpit, while the observer also had a prone position for observing in a ventral pannier. The undercarriage was jettisonable and the aircraft was fitted with floatation bags and hydrovanes to aid safe ditching, together with arresting gear to aid landing on aircraft carriers. The wings were detachable to aid storage. The prototype first flew in early 1921, proving to have poor flying characteristics, being described by Westland’s Test pilot, Stuart Keep as “a vicious beast”. Despite this, a further 35 were ordered.
The earliest American and British experiments were conducted using landplanes equipped with flotation bags in case of an emergency water landing. By the time of the Hibernia trials the Royal Navy was using seaplanes, which predominated in shipboard use thereafter until well into World War I. René Caudron and the Farman brothers in France, Glenn Curtiss in the United States, and the Short brothers in Britain all developed practical seaplanes by 1912. They quickly were joined by other designers, especially after the French industrialist Jacques Schneider established the valuable Coupe d’Aviation Maritime Jacques Schneider in December 1912 to encourage the development of seaplanes through international races to be held annually from 1913. Flying boats also developed rapidly, with very practical machines emerging from Curtiss, again, in the United States, Sopwith in Britain, the Franco-British Aviation Company in France, Lohner in Austria, and Oertz in Germany. Seaplanes, aircraft with float undercarriages, nevertheless predominated over flying boats, aircraft with boat-type fuselages, for shipboard operations.
Some further developments were very significant for the emergence of effective aircraft carriers. In 1913 the Short brothers patented their wing folding mechanism. This allowed them to reduce the stowed width of their seaplanes to as little as 12 feet and permitted rapid and trouble-free unfolding before flight, while maintaining structural strength for safe operation. This advance greatly increased the potential aircraft capacity of carriers, since the relative fragility of early machines required hangar stowage while at sea if they were to remain operational. In 1914, working very closely with Commander Charles R. Samson, in command of the Naval Wing of the Royal Flying Corps (usually known as the Royal Naval Air Service), and Captain Murray Sueter, head of the Royal Navy’s Air Department, Short produced more powerful versions of its folder seaplanes that were equipped to carry and drop torpedoes or bombs. This enabled the Royal Naval Air Service to conduct experiments in using its aircraft offensively. The greater load-carrying capabilities of these seaplanes also permitted experiments with wireless telegraphy communications, long-distance navigation over water, and some early trials of night flying operations.
Early in WWI the Royal Navy in the Canal Zone created two carriers “in theater” from German merchantmen interned at Port Said. Modifications to the Anne and the Raven II consisted of adding a 12-pound low angle gun for self defense and erecting canvas screens to protect embarked aircraft. These vessels initially operated under the Red Ensign with mixed naval and civilian crews and their first aircraft were up to six French Nieuport floatplanes apiece, originally operated by the French seaplane carrier Foudre, flown by French pilots with British observers, an extraordinary arrangement that worked very well in practice. During the summer of 1915 they were at last commissioned as Royal Navy vessels with naval crews and served until the later half of 1917.
The French Navy too created a seaplane carrier locally at Port Said in 1915 from a requisitioned French cargo liner, the Campinas. This vessel was very similar to the two extemporized British vessels and operated as many as ten Nieuport floatplanes. In home waters the French Navy also created a pair of seaplane carriers from cross channel packets. The Pas-de-Calais and the Nord acquired two hangers to accommodate two or three F. B. A. flying boats and were lightly armed. Their main distinction was their propulsion system- they were very unusual among aircraft carriers in being side-wheel steamers.
Navies placed considerable emphasis on the reconnaissance and gunfire observation missions from the outset. The Royal Navy’s first such aircraft was the Parnall Panther, whose design originated late in World War I as a dedicated carrier machine. It featured a wooden monococque fuselage that folded for stowage. Powered by a 230- horsepower Bentley B. R. 2 rotary engine, it attained a top speed of 108 miles per hour and had a maximum range of 350 miles. British carriers then embarked a series of three-seater biplanes from the Fairey Aviation Company, derived from a successful medium-size floatplane design that saw limited service during World War I.
Unlike other fleets, the Royal Navy also briefly deployed highly specialized gunnery observation aircraft equipped with facilities intended to maximize their effectiveness in this limited role. The first was the Westland Walrus, a much-modified variant of the Airco D. H. 9A light bomber featuring an observation cupola below the fuselage to accommodate the gunfire spotter. Powered by a 450- horsepower Napier Lion engine, it reached a top speed of 124 miles per hour and had a range of 350 miles. Its successors were the Avro Bison and Blackburn Blackburn. Both aircraft featured large cabins with good observation facilities to accommodate gunnery spotters and their equipment. Their Napier Lion engines gave them top speeds of 105 and 122 miles per hour respectively, while their maximum ranges were 360 and 440 miles. By 1931 the Royal Navy determined that the performance penalties of their accommodations and the burden of incorporating such specialized aircraft within the limited size of carrier air groups made further development of this category unnecessary, and the mission devolved on the fleet’s regular reconnaissance aircraft.
The French Navy too introduced dual-purpose observation and reconnaissance aircraft in 1928, when the Levasseur PL. 4 entered service aboard the Béarn. This three-seater biplane, with an all- metal structure, was powered by a 450-horsepower Lorraine 12eb engine, giving it a top speed of 111 miles per hour and a range of 560 miles. Its successor, the Levasseur PL. 10, entered service in 1932. Its 600-horsepower Hispano-Suiza 12Lb engine gave it a maximum speed of 137 miles per hour but its range fell to 450 miles.
The Imperial Japanese Navy gave up deploying carrier-based reconnaissance aircraft when the Mitsubishi C1M left front-line service in 1931. This aircraft was introduced in 1922 as the Type 10 Carrier Reconnaissance Plane, one of a trio of designs by Herbert Smith who came to Mitsubishi from the defunct Sopwith Aviation Company and created the navy’s first machines specifically designed for carrier service. It had a 300-horsepower Mitsubishi Type Hi engine giving it a top speed of 127 miles per hour and a range of 350 miles. Thereafter, until well into World War II, Japanese carriers relied on dedicated reconnaissance support from aircraft deployed on accompanying heavy cruisers and, to a lesser extent, on missions flown by their own attack aircraft.
Dedicated carrier reconnaissance types fared considerably better in the United States Navy. The Chance Vought Corporation produced a series of two-seater biplanes, derived from the successful VE-7 advanced trainer, that formed the backbone of the fleet’s carrier observation aircraft from 1922 until 1934. These machines started as all-wooden airframes and switched to steel tube fuselages in 1927. The original engine was a 200-horsepower Wright J-3 radial that gave the OU-1 a top speed of 124 miles per hour and a range of 400 miles. The improved O2U, powered by a 450-horsepower Pratt & Whitney Wasp radial engine, could reach 150 miles per hour and had a range of 600 miles, while the final SU-4, with a 600-horsepower Pratt & Whitney Hornet radial engine, had a top speed of 167 miles per hour and a range of 680 miles. An early Grumman Aircraft Engineering Corporation product, the SF-1, briefly supplemented these Vought types until 1936. This biplane aircraft, with an all-metal structure and powered by a 700-horsepower Wright Cyclone, featured a retractable undercarriage and could reach 207 miles per hour with a range of 920 miles. The real replacement for the Vought observation aircraft, however, was a series of scout-bombers, introduced in late 1935, that combined the scouting role with the dive bombing mission.
The most important proving grounds for testing tactics were the regular unit, squadron, and fleet-level exercises that all the carrier-operating navies conducted. Such exercises allowed naval aviators to explore new ideas and validated their concepts to squadron and fleet commanders so that the tactical possibilities offered by improved aircraft and weaponry could be incorporated into operational doctrine. In these venues carrier aircraft units demonstrated the efficacy of coordinated torpedo attack, dive bombing against fast-moving warships, tactical search missions, strike operations against shore targets, and distant reconnaissance. They also enabled fleet and squadron commanders to evolve effective combinations of carriers and escorting surface warships, and to develop concepts to integrate fast-moving carrier forces with battle fleet operations. These exercises also revealed the limitations of aviation: the vulnerability of carriers to tactical surprise brought on by deficiencies in search, the impact of weather, and, above all, the magnitude of the task of maintaining an effective defense against an enemy air attack. Navies discovered that it was very difficult to provide adequate fighter cover, since the warning time of an incoming attack was more often than not too short to allow quick launch of defending fighters while it was impossible to maintain a large enough standing covering force without crowding out attack aircraft from the carrier’s air group. This problem would not be solved until the advent of radar and accounts for the emphasis navies placed on striking fast and first with the most aircraft possible, the attendant diminution of fighter strength in favor of attack aircraft, and even the adoption of armored carriers by the Royal Navy.
To address the shortfall in carrier tonnage imposed by the Washington and London treaties, Japanese naval planners added to the fleet a number of modern auxiliaries whose design incorporated specific features allowing their relatively straightforward conversion into full-fledged aircraft carriers if required. A total of seven such vessels were ordered, three submarine depot ships (the Taigei, the Tsurugisaki, and the Takasagi) and four seaplane carriers (the Chitose, the Chiyoda, the Mizuho, and the Nisshin). All but two of the seaplane carriers (which were sunk while operating in their original role) were converted into carriers either before Japan’s entry into World War II or during the conflict.