Air force infantry are soldiers who are trained to fight on the ground, but they belong to the United States Air Force. The Air Force is a part of the military that uses airplanes and helicopters to help protect the country.
The Air Force infantry are like the superheroes on the ground. They go to intense training to prepare themselves to be able to fight in any environment. They learn things like how to use weapons, how to communicate with other soldiers, and how to survive when they are in dangerous situations.
When they are not fighting, the Air Force infantry helps to keep the military base safe. They are like the protectors of the base, making sure nobody tries to sneak in or hurt anyone.
So, basically, it's a group of soldiers who belong to the Air Force but are trained to fight on the ground and protect the base when they are not fighting.