 A linkless ammunition feed system was developed for the upgraded M61A1 installed in the F-104C; the M61A1 has subsequently been used by a wide variety of American combat aircraft.The cannon, mounted in the lower part of the port fuselage, was fed by a 725-round drum behind the pilot's seat.With its firing rate of 6,000 rounds per minute, the cannon would empty the drum after just over seven seconds of continuous fire.