an officer commissioned in a branch of the armed forces after an unusually short training period, especially after a three-months officers' training course during World War II.
Origin
1915-20, Americanism
Slang definitions & phrases for ninety-day wonder
ninety-day wonder
noun phrase
An Army or Navy officer commissioned after a three-month course at an officer candidate school
Any very youthful officer
A reserve officer put on active status after three months of training
Any person doing a job with minimal training •Usu used sarcastically: They sent us another ninety-day wonder to run the department