More than 160 U.S. and foreign military aircraft are catalogued in a U.S. Army manual (large pdf) which describes their distinctive physical characteristics in order to permit visual identification of the aircraft in flight.
The manual is nominally a restricted document, marked “for official use only,” and it has not been approved for public release. But a copy was obtained by Secrecy News.
Proper identification of aircraft is obviously a matter of military significance.
Incorrectly identifying a friendly aircraft (such as an F-15 Eagle) as an enemy aircraft (such as a MiG-29 Fulcrum) in wartime “could cause fratricide,” meaning the destruction of friendly aircraft, the manual states.
Conversely, incorrectly identifying an enemy aircraft (a Su-24 Fencer) as a friendly one (such as a Tornado) “might allow a hostile aircraft entry into, or safe passage through, the defended area.”
On the other hand, mistaking one type of hostile aircraft (a Su-17 Fitter) for another type of hostile aircraft (a MiG-21 Fishbed) would generally have “no impact” — except “if friendly countries were flying some aircraft types that are normally considered hostile.”
Likewise, mistaking one type of friendly aircraft (an F-4 Phantom) for another (an A-4 Skyhawk) would normally not be a great problem unless “a hostile country was using an aircraft type that is normally considered friendly.”
The manual covers both well-known and relatively obscure systems, but does not include classified aircraft.
Although an earlier edition of the manual was published without access restrictions, the current edition (2006) was not approved for public release.
But as the government imposes publication restrictions on an ever larger set of records, the control system seems to be breaking down at the margins, permitting unauthorized access with increasing frequency.
In this case, contrary to the restriction notice on the title page, the document does not reveal sensitive “technical or operational information,” in Secrecy News’ estimation.
See “Visual Aircraft Recognition,” U.S. Army Field Manual FM 3-01.80, January 2006 (413 pages in a very large 28 MB PDF file).
Update: Entropic Memes points out that there is reason to doubt the accuracy of some of the data in the manual.