Mickey Mouse Theater 1938 - King Neptune

Plot
King Neptune is holding court at the bottom of the ocean, being entertained by his various sea creature subjects. His favorites are a gaggle of mermaids (all brunettes with the exception of a single strawberry-blonde) who appear hand-sized next to the larger-than-life king.

Once dismissed from the king's presence, the mermaids surface to lounge on a rock and relax. They are spotted by a band of lecherous pirates who attempt to capture them using a lasso. The mermaids all escape apart from the strawberry blonde who is lassoed and pulled onto the ship of jeering pirates.

The frightened young mermaid is then attacked by the cruel pirates, jumping on her and pulling her hair, though she does a good job of fending them off. Enraged that one of his most beloved subjects has been taken hostage and suffering, King Neptune launches an assault on the pirates and a fantastic naval battle ensues.
The sea creatures work together to mimic such war machines as airplanes and bombs, submarine torpedoes, and other such modern equipment. During the attack one pirate drags the mermaid and puts her into a treasure chest to keep as a valuable.

The pirates do a fair job of fending off their attackers, so Neptune rises to the surface and summons a storm while stirring up huge whirlpools with his trident. In the end, he jumps on top of the pirate ship, plunging it straight to the bottom of the ocean.