Simplify the following text for a Grade 7 native English-speaking person.
Original: During World War II , Thompson served in the Royal Canadian Air Force and doubled as the coach of the Calgary RCAF Mustangs of the Alberta Senior Hockey League .
Simplified: During World War II , Thompson served in the Royal Canadian Air Force ( RCAF ) . He was also the coach of the Calgary RCAF Mustangs of the Alberta Senior Hockey League .