 Prior to this, when the only practical means of transferring fuel was through a hose, other crew members fulfilled the duty of operating the air refueling equipment, such as the hose reel operator in the DH-4B and C-1 and the line operator in the B-24D and KB-29M using the grappled-line looped hose system.In the modern U.S. military, the boom operator crew position only exists in USAF tankers equipped with a flying boom, such as the KC-135, KC-10, and the newly-developed KC-46.For tanker aircraft not equipped with a flying boom, such as the KC-130, HC-130, and F/A-18E/F, the specific crew member(s) responsible for operating the air refueling equipment and supervising refueling operations varies by aircraft.