Buddy packs are external fuel tanks attached to an aircraft, allowing it to deliver fuel to other planes in midflight. Midflight refueling radically expands the range of aircraft and can be especially useful in wartime, when planes would otherwise be tethered to an airfield or carrier group. In the case of the buddy pack, the tanks are fitted to an ordinary plane, eliminating the need for a specialized plane just for midflight refueling and cutting down on operating costs for the mission.
Also known as buddy stores, buddy packs can be strapped to various sections of a plane's fuselage or wings. When loading planes, the distribution of weight must be considered, along with the risks of ruptures to the tanks, creating a potentially hazardous situation in flight. Many planes are equipped to drop the tanks after they are empty or in situations where carrying tanks filled with fuel could pose a safety risk.
The buddy packs are attached to hosing used for midflight refueling. Planes in need of fuel link up with the aircraft and the fuel is directed into their tanks. Carrying tanks of fuel adds to the weight of a plane, limiting the amount of time it can spend in the air, and it will have to loop back to the base to refuel itself after delivering fuel to other planes in the group. The added fuel from buddy packs allows other planes in the group to keep going, continuing reconnaissance and other missions.
Flying with buddy packs requires some special training. The pilot needs to be able to handle a heavier and usually less maneuverable plane comfortably. In addition, pilots have to be familiar with midflight refueling procedures. This process requires a high degree of control over the aircraft, as planes need to fly close together and hold formation while the refueling takes place.
A related concept is the drop tank, a tank carried to extend the range of an aircraft. Drop tanks are intended for use by the aircraft carrying them, rather than for midflight refueling, and they were used extensively during the Second World War, when planes had to travel great distances. Usually, the tanks were dropped as soon as they were empty to lighten the load on the plane. Planes might also be ordered to drop laden fuel tanks before landing due to concerns about fragility; the British made drop tanks from paper, for example, and landing with laden tanks could have created a significant explosion.