This short was released just over a month before the U. S entered WW2 after the attack on Pearl Harbor. Once wartime censorship standards were imposed, no more than three of any weapon or vehicle (plane, ship, tank, etc) could be depicted in a photographic or film image. This short, made just before the war, shows fleets of U S. Army Air Corps planes, both on the ground and in the air.
The little single engine plane Barney flies still bears the symbol of the U. S. Army Air Corps, and likely may have been used to tow targets for artillery practice.
Pelicans really can (and do) dive straight into the water to catch fish. That ability is shown here as the bird and plane do combat. One of the collective names for a group of Pelecanus is, appropriately, a squadron.