In early 1942, at the age of 22, he flew a Mitsubishi A6M Zero with the Lae-based Tainan Air Group.

There the young petty officer, 1st class became one of the so-called "Clean-up Trio" of Japanese aces, along with his squadron mates Saburo Sakai and Hiroyoshi Nishizawa.

Ōta's first confirmed kill, of a U.S. Army Air Force P-40E Warhawk, was over New Guinea on April 11, 1942.

Ōta is credited with 34 victories, making him the Imperial Japanese Navy's fourth-ranking ace.

In his autobiography, Sakai described Ōta as outgoing and amiable, in contrast to the more reserved Nishizawa, and said he would have been "more at home in a nightclub" than in Lae.