|Role||Patrol flying boat|
|Manufacturer||Hiro Naval Arsenal|
|Primary user||IJN Air Service|
Design and development
First appearing in 1931 the H4H1 was a twin-engined high-wing monoplane flying-boat. Powered by two 500 hp (597 kW) Hiro 91-1 engines strut-mounted above the wing it was produced by the Kawanishi company and entered service in 1933.
An improved version of the design, the H4H2, followed into production two years later. The H4H2 has re-designed twin fins and rudders and was powered by two 800 hp (597 kW) Myojo radial engine. A total of 47 of both versions was produced.
Both the H4H1 and H4H2 remained in front-line naval service through the 1930s.
- H4H1 (Hiro Navy Type 91 Model 1 Flying Boat)
- Variant powered by two 500hp (597kW) Hiro 91-1 engines.
- H4H2 (Hiro Navy Type 91 Model 2 Flying Boat)
- Variant powered by two 800hp (597kW) Myojo radial engines.
Data from 
- Length: 54 ft 4¼ in (16.57 m)
- Wingspan: 76 ft 11½ in (23.46 m)
- Height: 20 ft 5 in (6.22 m)
- Wing area: 890.20 ft2 (82.70 m2)
- Empty weight: 10280 lb (4663 kg)
- Gross weight: 16534 lb (7500 kg)
- Powerplant: 2 × Myojo radial piston engine, 800 hp (597 kW) each
- Maximum speed: 145 mph (233 km/h)
- Range: 793 miles (1260 km)
- Service ceiling: 11880 ft (3620 m)
- 1 × 7.7mm (0.303in) Machine Gun (mounted over bow cockpit)
- 2 × 7.7mm (0.303in) Machine Guns (mounted over midship cockpit)
- 2 × 250kg (551lb) bombs
- Orbis 1985, p 2173
- Illustrated Encyclopedia of Aircraft (Part Work 1982-1985). Orbis Publishing.