In the U.S. Air Force (USAF), a boom operator is an aircrew member aboard tanker aircraft who is responsible for safely and effectively transferring aviation fuel from one military aircraft to another during flight (known as "aerial refueling", "air refueling", "in-flight refueling", "air-to-air refueling", and "tanking"). The name boom operator implies that one "operates a boom" (the "flying boom"), which is a long, extendable metal arm attached to the rear underside of the "tanker" that the boom operator connects to the fuel receptacle of a receiving aircraft (the "receiver"). The boom operator also controls the refueling "drogue", a basket attached to a flexible hose that trails the tanker, when using the probe-and-drogue system. The USAF officially designates the boom operator career field as "In-Flight Refueling" with a specialty code of 1A0X1. However, this designation is usually reserved for administrative paperwork such as enlistment contracts and performance reports, as boom operators themselves are rarely referred to as in-flight refueling specialists within the USAF. The title "Boom Operator" is most commonly used, in reference to the aircrew position they occupy on the airplane, as noted in USAF regulations and aircraft flight manuals. Fellow crew members affectionately address them as "boom" or "boomer" (though the use of the term "boom" in this article refers to the flying boom, not the boom operator).