The H8K3, designated as the Type 2 Large Flying Boat, Model 22 (二式飛行艇二二型), was a prototype intended to improve on the main-production H8K2 by enhancing flight performance through reduced air drag. Its primary modification was the addition of retractable wing pontoons and dorsal gunner. Further changes included additional armor to protect the central fuselage fuel tanks. These and other modifications increased the aircraft’s weight by 2 tons. Unfortunately, the added weight offset any aerodynamic gains, leaving overall performance unchanged while water handling worsened. Due to these limited performance improvements, only two prototypes of the Model 22 were produced which later were re-engined to become H8K4 Model 23s. These prototypes were operated by the 801st Air Group and were often mistaken for B-24 "Liberator"s due to their silhouette with the pontoons retracted.

Introduced in Update 1.57 "Battle March", the H8K3 performs surprisingly better than the H8K2 in terms of acceleration in-game due to the decreased drag. With its additional armor, the H8K3 is even more formidable in battle, resulting in a difference in Battle Rating. Bomb load, armament, and other performance features remain unchanged, so it otherwise handles similarly. Use it to bomb bases, ground targets, or naval targets while relying on its formidable defenses to fend off pursuers.