Japanese 40mm Ho-301 ease/ess. Note projectile standing on magazine (Courtesy: MoD Pattern Room)
(Myrt) - two Type 99-2; or one 30mm Type 5, D4Y (Judy) - one Type 99-2; and J2M (Jack) - two Type
99-1, as well as the IJAs Ki-84 (Frank) - three 20mm Ho-5. Twin-engined naval aircraft with upward-firing guns included the J1N1 (Irving) -two Type 99, and P1Y1 (Frances) - four Type 99. The 1JA aircraft were the Ki-45 (Nick) - two 20mm Ho-5; Ki-46 (Dinah) - one 37mm Ho-204; and Ki-102 (Randy) - two Ho-5. The J1N1 -S (Irving) actually had four obliquely mounted 20mm cannon in the fuselage - two firing upwards, two downwards.
Complete information about which models of Type 99 were used in upward-firing installations is not available. The most common weapon was probably the Type 99-1 Model 3, which was fitted with a
100-round drum, but the belt-fed Model 4 and the Type 99-2 were used where there was space for them.
Perhaps the most remarkable armament fit belonged to the twin-engined Kawasaki Ki-45-Kai-C (Nick), which reportedly mounted one forward-
firing 37mm Ho-203 (with a fifteen-round belt feed) in the nose, a forward-firing Ho-3 in a ventral tunnel, two upward-firing Ho-5 inside the cockpit, and an RCMG for the observer! Other reports state that the Ho-3 was in practice removed when the Ho-5s were fitted.
The UN also experimented with obliquely mounted guns for ground attack. The P1Y (Frances) was fitted with up to seventeen downward-firing Type 99 guns in the bomb bay, twelve angled forwards, five rearwards. Thirty of these aircraft were being prepared for attacking B-29 bases and for sweeping landing craft during amphibious assaults, but the war ended before they could see service.
