In 1917, Wilkie and Mitchell are inept lifeguards attempting to avoid the war.  When a man is drowning, they allow Hogan, who is a tough sergeant in the Army Air Corps, to rescue him because they cannot swim, and they then take credit for the rescue.  At a Red Cross benefit boxing match, Wilkie and Mitchell encounter Hogan, who is billed as "One Punch" Hogan, and when Hogan sees Wilkie, he starts a fight, but Wilkie knocks him out.  As a crowd gathers, Wilkie and Mitchell sneak out, swearing they will never join the Army.

Later, Wilkie and Mitchell are indeed in the Army, shoveling manure.  Disgusted by their situation, they decide to quit and go to South America, and hop onto a manure truck that is leaving the base.  They stowaway on a ship, unaware it is a troop ship carrying Army Air Corps pilots to France, and ask the first person who passes by them for food.  Unfortunately, that person is Hogan, who turns them over to the commanding officer.

Wilkie and Mitchell are sent to the American aviation field in France after claiming they wanted to join a flying unit.  There, they adroitly avoid flying the planes during training, especially after Mitchell's first disastrous solo attempt.  While on guard duty, Wilkie competes with Hogan for the attentions of Fifi, a French performer.

Later, Wilkie visits Fifi and her friends at a nightclub, and when Hogan comes after him, they fight.  The police arrive, and Hogan and Wilkie make a quick exit, then hide in American Mary Way's car.  Startled by their appearance, she crashes the car, and unharmed, they escort her to an inn for the evening.  In the morning, Wilkie has breakfast with Mary and cons Hogan into fixing her car.  Military police come looking for the two men and arrest them, as well as Mary, whom they think is a spy.

Wilkie, Hogan and Mary escape, fly a plane off base, land in enemy territory and are captured.  Along the way, however, they release two bombs to drop excess weight and unwittingly bomb a major German munitions depot.  The Air Corps colonel sends a squadron to rescue the trio, and the first to arrive is Mitchell, who terrorizes the Germans by his inept maneuvers.

After their rescue, the three fly home as heroes, and while relating his story to Mitchell, Wilkie accidentally pulls the lever for the bomb hatch and bombs his own base.