This is an Airborne trucker hat, inspired by the 101st Airborne Division, a light infantry division with the US Army, assigned to Vietnam (circa 1967 - 1975).
The 101st Airborne Division, dubbed the 'Screaming Eagles', operated in Vietnam independently as sort of a fire brigade and earned the reputation as being called the "Nomads of Vietnam." The 101st fought in every area of South Vietnam from the Demilitarized Zone up north and all the way down to the Central Highlands. The 101st was deployed in the northernregion operating against the People's Army of Vietnam (PAVN) infiltration routes through Laosand the A Shau Valley for most of the war. Notable among these were the Battle of Hamburger Hill in 1969 and Firebase Ripcordin 1970.
Also called the 'Chicken Men' by the North Vietnamese because of their insignia, enemy commanders have been said to have warned their men not to engage the 'Chicken Men' at all costs because they were a sure to lose any engagements with them.