While en route to Kadena Air Base in Okinawa, Japan, on Saturday, a navigation software issue was discovered, said the 13th Air Force, which is headquartered at Hickam Air Force Base.

All aircraft, which had departed Hickam earlier that day, returned safely. Officials expect the 12 aircraft will depart Hickam within the next several days.

"This is a minor issue, and, since our focus is always on safety, the aircraft will not depart until we are confident there are no further issues with the navigation system," said Lt. Gen. Chip Utterback, 13th Air Force commander.

The Air Force said it is deploying the dozen Raptors and more than 250 personnel from the 27th Fighter Squadron, Langley Air Force Base, Va., to Kadena as part of a regularly-scheduled U.S. Pacific Command rotational assignment of aircraft to the Pacific.

F-22A engineers and maintainers are working to update the software. After successful testing, the aircraft will continue their planned first overseas deployment to Kadena, the Air Force said.

The aircraft, whose angular shape and internal weapons bays contribute to a radar signature the size of a bird, is one of the costliest fighters ever at more than $339 million a copy, including research, development and testing. The per-plane production cost is about $135 million.

High costs forced the F-22 program to be scaled back, and 183 are scheduled to be built. Original plans called for 750. The F-22's sophisticated avionics are the first to integrate radar, weapons systems, communications and navigations to give the pilot better situation awareness.

The stealthy Raptors last week made their first stop in Hawai'i on their way to Japan. The Air Force plans to base 20 of the fighter aircraft at Hickam starting in late 2010.

The Raptors can reach supersonic speed without afterburners, are highly maneuverable and are practically invisible to radar.

The Hawai'i Air National Guard will be the first Guard unit to "own" the Air Force's most advanced weapons system, while the active duty Air Force at Hickam will be an associate unit and also fly and maintain the aircraft.