The Gremlins

The Gremlins was a planned Disney film, based on a 1943 Roald Dahl book.

Plot
Mythical Gremlins are blamed for causing mechanical problems for pilots in the British Airforce during the Ssecond World War.

Why It Was Cancelled
Warner Brothers released the Bugs Bunny short Falling Hare the same year using the same premise.

Result
Two screenplays were written, and a promotional book was released before the project was put aside.