The dramatic advances made in aeronautics after WWI gave rise to many innovative designs that led to new uses for airplanes in naval combat.
Many countries which were surrounded by water began development of planes fitted with floats which could take off from water or be launched from catapults on warships. They were used for reconnaissance and in a defensive role against surface and submarine vessels, with the opinion being that these were the limits of floatplanes. The only country to use floatplanes more widely was Japan. Although the idea wasn’t new and had been attempted by other countries, the Japanese were the first to design and mass produce a float-equipped fighter and use it in combat.
During the attack on China the Japanese naval air forces were very successful at quickly establishing air superiority. A side effect of the invasion, however, was to convince the Japanese command of the need to ensure access to strategic natural resources such as crude oil, rubber and iron ore if they were to continue waging war. Those resources were readily available on the islands of the southwest Pacific, and would be easy enough to capture, but doing so would put Japan at war with Great Britain, Holland and the United States. It was clear to the Japanese command that once islands were captured they would serve as bases for further attacks and airfields would need to be built. On the larger islands in the region the Allies already had airfields. Taking this into account, the Japanese planned to use the smaller islands and atolls in less protected regions for their airfields as well. The sheer size of the arena at hand limited the use of aircraft carries to a few operations at once, and it was imperative that amphibious groups have air cover for landing operations, even if land-based airfields weren’t ready yet. Some kind of defense was also needed while the fleet was carrying on offensive maneuvers in other areas of the Pacific. The “15-Shi” specification for a float-equipped fighter was laid out by Kaigun Koku Hombu (Navy Air Headquarters) in September, 1940 for use on atolls and small islands that were too small or the terrain too unfriendly to support an airfield. It was to be a single-engine, single-seat fighter powered by a single radial engine with one main float and two helper floats. The contract was awarded to Kawanishi in the hope that they would be able to quickly come up with a design. Kawanishi assigned the N1K1 project to a group of engineers including Toshihara Baba, Shizuo Kikuhara, Hiroyuki Inoue and Elizaburo Adachi. Although they were very enthusiastic about the project the prototype turned out to be difficult to build. The engineers planned to use a powerful 1,460 hp Mitsubishi engine that would turn two contra-rotating two-bladed propellers but had problems with the gear box. Kaigun Koku Hombu was getting more impatient as war drew closer, and the final version of the plane wasn’t even on the drawing table yet. Over a year and a half had passed when the contra-rotating propellers were finally removed in favor of a single three-bladed propeller. The N1K1 prototype flown in May, 1942 flew well but Kawanishi’s production strength was too small to put the plane into full-scale production. A total of eight prototypes and 89 production models were built.
In the meantime, Kaigun Koku Hombu was pressed for time and decided to examine the possibility of adapting an existing fighter to a floatplane. At the time the best fighter in the Imperial fleet was the recently introduced Mitsubishi A6M2 Model 21 which had literally hammered the enemy competition in China. The decision to make a floatplane version of it according to the “15-Shi” specifications and modifications included in “16-Shi.” At that time Mitsubishi was working at full capacity on other projects, so the decision was made to subcontract the work to Nakajima Hikoki K. K. in Ota, where they had just started making the Zero under license, and the design offices had the necessary resources available for the project.
In February, 1941 two engineers, Niitake and Tajima started work on a project called AS-1. Nakajima had been building aircraft for the Japanese army, and had come up with successful fighters such as the Ki-27 or Ki-43. A very successful shipboard torpedo bomber, the B5N was designed for the Navy, but with a traditional undercarriage. So the project wasn’t going to be easy, and the engineers would have to study the dust-covered notebooks of their predecessors.
After examining different possibilities, it was decided that the A6M2 would be an ideal candidate for floats, with little change necessary needed for the conversion. The main work was in designing the floats and how best to mount them. The result was an almost unchanged original with added floats called the A6M2-N.
The wings were not hinged and were made up of two main beams and thirty ribs. The wing dihedral was 5° 40’ with a tapered-rounded shape and the wingtips each had two ribs. For technical reasons the spars were not made in a single piece but were butted between the 12th and 13th ribs and joined with angle plates, screws and rivets. Longerons were used to stiffen the skinning. Two fuel tanks were mounted in each wing. Stress skin was flush-riveted smooth duralumin. Metal-framed, cloth-covered ailerons 3,283 mm long with trimming tabs were mounted on the trailing edge of each wing by three hinges attached to the rear beam. Split flaps (metal with wooden reinforcement at trailing edge) 1,595 mm long were attached to the rear beam. Two 20 mm Type 99 Model 1 Mk3 cannon were mounted in the wings and fed by drum magazines which held 60 rounds each. The magazines were replaced through access panels on the upper wing surfaces. On the lower wing surfaces (next to the cannon) were two racks for 60 kg bombs. The landing gear was completely removed and the wheel-wells were faired over. Two cantilever stabilizing floats were attached under the wings about 1/3 of the wing length from the tip. The completed wing sub-assemblies were then mounted to the fuselage with the skin forming the cockpit floor.
The fuselage, like that of the A6M2 was in three parts. The first part was the engine housing and contained the Nakajima Sakae 12 fourteen-cylinder air-cooled radial engine which produced 953 hp for take-off. It was coupled with a supercharger which was driven by a step-up gear connected to the shaft and delivered the correct amount of pressure to the suction manifold. It was attached to the bearer support struts on the firewall bulkhead. The bearer support was a ring of welded tubing with thirteen attachment points for the engine and four welded, V-shaped struts attached to the bulkhead. The base of each V-shaped strut had a 16 mm flange for bolting the struts to the bulkhead. The carburettor intake was located at the base of the cowling nose ring. The propeller was a three-blade Sumitomo (a licensed Hamilton Standard CS 40B) measuring 2.9 m in diameter and was adjustable from 25° to 45°.
The rest of the fuselage could be treated in two parts which were strengthened by four main solid longerons (two upper and two lower) flush-riveted to the skin.
The forward section, from the bulkhead to former #7 (at the wing trailing edge), was semi-monocoque with stress skinning that contained integrated, molded channeling which formed the second, fourth and fifth formers. It was also where the pilot’s seat and turnover truss was mounted. Duralumin stringers were used to stiffen the construction. The forward section was joined to the wing assembly at the factory and formers #4 and #7 were attached to the wing main beams. Former #7 had 80 holes for 5 mm screws spaced approximately 40 mm apart for joining to the rear fuselage section. The fuselage fuel tank and a 60 liter oil reservoir were located behind the firewall which raised the fuel capacity to 518 liters. None of the fuel or oil tanks were self-sealing. Two belt-fed 7.7 mm Type 97 machine guns were mounted above the tanks with 500 rounds each. The machine gun mechanisms extended through the firewall into the cockpit, which made reloading easier in case of jamming.
The cockpit was situated between formers #2 and #5. The pilot’s seat was stamped duralumin and was adjustable vertically. The oxygen tanks, radio (Type 96 Ku-1, range 90 km) and a Type 1 Ku-3 battery powered radio direction finding unit were located behind the pilot’s seat. Flight and engine controls were located on the instrument panel, while to the right of the pilot’s seat was a hand pump for the fuel system. Control surfaces were controlled by a one piece stick and rudder bars. The cockpit was protected by an organic glass canopy which slid aft. A Type 98 reflective sight was mounted behind the windscreen and the weapons trigger was located in the throttle control.
The rear fuselage thinned to an oval shape and was integrated with the tail section which was attached to former #16. Some modifications were made to the tail section, which included removing the tail wheel and arresting hook and mounting a stabilizing fin. The rear fuselage was closed off by a two-part tail cone that extended the line of the tail fin.
The empennage was cantilevered and fixed to the fuselage except for the elevator leading edges. Control surfaces were framed in metal, fabric covered and controlled by linked cables. The rudder had a symmetrical profile and was keyed to the fuselage at a 90°. The rudder post was attached to former #16, guided by three hinges and equipped with a rudder tab. The tailplane was twin-spar with a span of 4.7 meters. It was keyed to the fuselage at 1°. The metal framed, fabric covered elevators with trim tabs were hinged to the rear spar.
The most obvious modification was the large main float attached under the fuselage. It was of all-metal construction with bulkheads strengthened by stringers. The upper section was oval in shape and the lower section had two concave halves which met in line with the center of the airplane. At the three lowest points of the float and at the rear were stabilizing fins that extended out. The center section of the float contained a 330 liter fuel tank as a replacement for the belly tank used on the carrier version of the A6M2. The float was attached to the fuselage by a large forward-sloping pylon in front and a thinner V-shaped strut at the rear. The pylon housed an air intake for the oil cooler (housed behind the engine firewall) and the fuel lines to the float tank. The V-shaped strut was mounted perpendicular to the cockpit and in line with the rear wall.
The prototype was completed at the end of November, 1941 and had its maiden flight on December 8 (Dec. 7 in Hawaii), the day that war broke out in the Pacific. The first few trials revealed that changes would need to be made to the main float to increase the stabilizing effect of the fins. Three more prototypes were built and underwent intensive test till march, 1942.
The increased weight and drag reduced the top speed of the plane to 440 km/h. In spite of this, the floatplane retained the maneuverability and stability of its predecessor and Kaigun Koku Hombu was more than satisfied with the results. Because the Allies had no bombers or reconnaissance planes capable of greater speeds, it was felt that this floatplane would be a competent fighter against them and the A6M2-N was ordered into production. It was designated the Type 2 Floatplane Fighter Model 11 or Ni-Shiki Suijo Sentoki.
Production began in April, 1942 and was limited to twelve planes per month during the first stages. Half of the finished planes were sent to the Aleutians, and the other half were sent to the Solomons. The plane’s further development wasn’t made a priority since most felt that the Kawanishi N1K1 “Kyofu” would soon enter production as a replacement. There were hopes that both pilots and ground personnel trained on the A6M2-N would be quickly retrained for the N1K1. As it turned out, by the time the “Kyofu” entered production the Japanese had practically lost the war in the Pacific.
The only modification made to the A6M2-N during production was to replace the propeller with a more conical one. It’s impossible to say exactly how many planes had the new propeller, but it’s estimated that no more than 120 were built. A small increase in production meant that 15-20 planes were built monthly, and by September, 1943 when A6M2-N construction was stopped, a total of 327 had been built. They were used by Kajima, Otsu Sasebo, Toko and Yokohama Kokutai and by 5, 14, 36, 452, 801, 902 and 934 Kokutai as well as by Kamikawa Maru Suisentai.
Nippon Sea Falcons
A leutian Islands. At the beginning of June, 1944, Japanese landing forces occupied two islands – Attu and Kiska – in the Aleutian Islands. The islands were American territory, but the occupation was more useful for Japanese propaganda than for military strategy and was meant to be a comfort after the disgraceful disaster at Midway. On these small, northern islands was little more than fog, wind and bare rock. It would have been senseless to build airfields there, but the Japanese garrisons were within reach of the American bases at Dutch Harbor. To give the Japanese troops air cover at Holtz Bay, it was decided to form a base of float planes including the debut A6M2-N. The 5 Kokutai was picked for the mission and was renamed 452 Kokutai, which arrived at Kiska on June 15 together with six A6M2-Ns which were soon assigned the code name Rufe by the Allies.
The A6M2s weren’t the only Japanese air forces in the area. Also at Kiska was 5 Koku Kantai (2nd Air Fleet) which was equipped with observation seaplanes from Chuchijima Kokutai and four-engined Kawanishi H6K4 Type 97 “Mavis” flying boats from Toko Kokutai.