Wild Eagle Boys Unit

(from ebookjapan):

The year is 1940. Ken Furushiro endures rigorous training at the Preparatory Training Camp, dreaming of becoming the Battle 0 pilot of tomorrow. When he sees that his best friend Bunya has deserted with a bang, he can't leave him alone! He followed him in the same red dragonfly, but encountered a mysterious submarine at sea. Ken, who dreamed of becoming a great pilot like his brother, successfully defeated the enemy, but one day he heard an unbelievable news. His older brother, Major Furushiro, had suddenly disappeared in China and escaped!