Thunderbolt 33 (j2m5): on May 20, 1944, the test flight was successful, equipped with" Mars "26a engine, and the power system was greatly improved. On September 28 of the same year, in the test flight, the maximum speed reached 615 km / h, and it took only 9 minutes and 45 seconds to climb to 8000 meters, which was the highest in Wartime Japanese fighters. At that time, the B-29 had launched a large-scale air attack on Japan, and the navy was eager to produce the modified model. However, due to factory evacuation and other reasons, only more than 30 were produced. In addition, there was an improved plan to refit 30mm large caliber machine guns, but it was not implemented