The result of years of experimentation by the Imperial Japanese Navy, the Mitsubishi A6M Reisen is perhaps the best known Japanese World War II fighter type. The Zero, or "Zeke," in official Allied reporting, saw action in practically all battles waged by the Imperial Japanese Navy, from the attack on Pearl Harbor all the way through the defense of the Home Islands against the B-29s. During the first months of the war in the Pacific the Zero emerged as a world-class fighter, unrivaled in the air by anything the enemy could muster. However, with no worthy successor in sight, by 1943 the Zero was all but obsolete. Despite that, Japanese factories continued to build and deliver the type until the end of the war.