Type B Kō-hyōteki-class Midget Ha 45 prototype built 1942 to test Type A improvements.[30] Type C Kō-hyōteki-class Midget Ha 62–76 similar to Type A with crew of 3 and radius increased to 350 nautical miles (650 km) at 6 knots (11 km/h) surfaced or 120 nautical miles (220 km) at 4 knots (7.4 km/h) submerged.[30] Type D Kō-hyōteki-class, also called Kōryū class (115 completed) improved Type C with crew of 5 and radius increased to 1,000 miles (1,600 km) at 8 knots (15 km/h) surfaced and 320 miles (510 km) at 16 knots (30 km/h) submerged.[31] Kairyū-class submarine Kaiten submarine suicide torpedo.