armor-glass canopy, 13 mm (.51 in) of head and back armor, and multiple bulkheads in the fuselage, which protected both the methanol-water tank (used to increase the effectiveness of the supercharger) and the centrally located fuel tank. It was the Nakajima firm's own-designed displacement, Ha-45 Homare ("Praise" or "Honor") air-cooled eighteen-cylinder radial engine, first accepted for military use in 1941, that gave the Hayate its high speed and prowess in combat. Derived from the Nakajima Homare engines common to many Japanese aircraft, the Hayate used the Homare 21 direct-injection version of the engine, using water injection to aid the supercharger in giving the Ki-84 a rated 1,491 kW (2,000 hp) at takeoff. This combination theoretically gave it a climb rate and top speed roughly competitive with the top Allied fighters. Initial Hayate testing at Tachikawa in early summer 1943 saw test pilot Lieutenant Funabashi reach a maximum level airspeed of 624 km/h (387 mph) in the second prototype. In 1946, US Technical Intelligence tested a Homare Model 21-engined Hayate and achieved a speed of 687 km/h (427 mph) at 20,000 feet using 92 octane AvGas, plus methanol injection. The complicated direct-injection engine was a compact design (only larger in diameter than the Ki-43's 14-cylinder Nakajima Sakae radial) that required a great deal of care in construction and maintenance and it became increasingly difficult to maintain the type's designed performance as the Allies advanced toward the Japanese homeland. To compound reliability problems, the Allied submarine blockade prevented delivery of crucial components, such as the landing gear. Many landing gear units were compromised by the poor-quality heat treatment of late-war Japanese steel. As a result, many Hayates suffered strut collapses on landing. Further damage was caused by inadequately trained late war pilots, who sometimes found it difficult to transition to the relatively "hot" Ki-84 from the comparatively docile Ki-43, which had a significantly lower landing speed. Operational service The first major operational involvement was during the battle of Leyte at the end of 1944, and from that moment until the end of the Pacific war the Ki-84 was deployed wherever the action was intense. The 22nd Sentai re-equipped with production Hayates. Though it lacked sufficient high-altitude performance, it performed well at medium and low levels. Seeing action against the USAAF 14th Air Force, it quickly gained a reputation as a combat aircraft to be reckoned with. Fighter-bomber models also entered service. On