When the U.S. Air Force retired it's F-4 fighters
in the 1980s, it converted many of them to UAVs, to serve as aerial
targets. These aircraft became the QF-4, and the air force is running
out of them. There are only about fifty left, and training operations
destroys about 25 a year. The existing supply of decommissioned F-4s
will keep the air force going until about 2011. Before that, it will
start turning retired F-16s into QF-16s.
the QF-4, the air force had converted F-100s (218 of them), F-102s
(136) and F-106s (210) to act as full scale target aircraft. There are
smaller UAVs that are used as small scale targets. The full scale
models were needed to test the capabilities of new, and existing,
missiles. Nothing like using real missiles against real targets to
build pilot confidence, and be sure the damn things work.
QF-4s can be flown with, or without, a pilot on board. The aircraft use
GPS to help with navigation, and to insure that QF-4s flying in
formation don't collide with one another. The aircraft also carry
sensors to detect near misses by missiles.