Double Bar. The double bar symbol is used to denote certain kinds of norms in mathematics (e.g., or). It is also used to denote parallel lines, as in, and in an older notation for the covariant derivative. In this work, the notation or is reserved for matrix and function norms, respectively.
The F-4 Phantom II remained in use by the U.S. in the reconnaissance and Wild Weasel (Suppression of Enemy Air Defenses) roles in the 1991 Gulf War, finally leaving service in 1996. It was also the only aircraft used by both U.S. flight demonstration teams: the USAF Thunderbirds (F-4E) and the US Navy Blue Angels (F-4J).
Iran Air Flight 655. Iran Air Flight 655 was an Iran Air passenger flight from Tehran to Dubai. On 3 July 1988, the aircraft operating on this route was shot down by the United States Navy guided missile cruiser USS Vincennes under the command of William C. Rogers III. The incident took place in Iranian airspace, over Iran's territorial waters in the Persian Gulf, and on the flight's usual flight path.