The XF-85 was intended to give fighter protection to 'parent' B-36s by carrying the 'parasite' within the bomb bay, lowering and releasing it from a trapeze as required. Testing with a modified B-29 began in 1948 but about half of the Goblin flights ended with emergency ground landings after the test pilot could not re-hook to the B-29. The program ended when aerial refueling of conventional fighter aircraft showed greater promise.