Natick Labs designed the tropical combat jacket and trousers in 1962 following a request from Army Material Command for a specialized uniform for Special Forces personnel in Vietnam.1 The single-breasted jacket was made from 5½ oz. wind-resistant cotton poplin in OG-107 and featured two slanted chest cargo pockets and two lower cargo pockets. The design also boasted epaulets, waist take-in tabs, pen pockets behind both chest cargo pockets and an inner gas flap that was designed to prevent chemical agents leaking through the front button closure.
The tropical combat uniform was ideally suited to Vietnam because it was both lightweight and quick drying, but it's exposed pocket buttons had a tendency to get snagged in the jungle.
1. Support To United States Army In Vietnam - Clothing & Equipment (United States Army Material Command Feb 1967)