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).
A U.S. Navy Grumman Panther of the kind used to shoot down 4 Russian MiG 15s on Nov 18. 1952. A Russian Su-24 Fencer, a multi-role attack aircraft, was shot down by Turkish F-16s while reportedly flying in Turkish airspace Tuesday. The shoot down â while having wide-ranging ramifications for countries operating in the region â marks the first time a NATO country has shot down a Russian jet in just over 63 years.