M25 is the ENIGMA designation of a former radio communications network, operated by the United States Government.
Information about this radio network was first published by Harry Helms, W5HLH,  in 1980. Helms stated that is was an operation of the State Department Intelligence Service (possibly meaning the Bureau of Intelligence and Research). He listed the following stations:
- KKN50 - Washington DC
- KRH50 - London, UK
- ACN - La Paz, Bolivia
- KKN44 - Monrovia, Liberia
- KWS78 - Nicosia, Cyprus
The stations intially operated in Morse code while later they started using RTTY as well.
Don Schimmel published a QSL card sent in 1985 to Patrick O'Connor by KKN44 , on which the station is idntified as "Regional Relay Facility, Monrovia, Liberia, Diplomatic Telecommunications System". Schimmel added a new station to the list, KKN39 in Miami, FL and corrected the location of KWS78 as Athens, Greece.
According to Ary Boender , officially, KKN50 was operated by the National Communications System (NSC) for the US Department of State. KKN50 used at least one of the facilities of the Warrenton Training Center (WTC). Warrenton has/had five sites, 'Station A', 'Station B', Station C', Station D', and 'Station E'. WTC 'Station C' is located near Remington and is one of the homes of 'The Counting Station' [E05/V05]. The Office of Communications (OC) used 'Station D' at Culpepper, VA, as relay center and it was also the site that was used by KKN50.
KKN50 was the master station of a global network. In official publications the stations were often listed with fake locations. A couple of the most active stations have been figured out over the years, though. One of the most active stations, besides KKN50, was OC Miami with callsign KKN39. Their routing indicators were RUEG and RUEGMI. Incidentally, the tactical call of KKN50 was BRANDY and its routing indicator was RUES. KKN44's signal was also found as part of Voice of America's feeder signal.
The network was last heard in 1997.
The main players in the net were:
|Callsign||Location||Frequencies (kHz)|| Sound|
|KKN50||Washington DC, USA||6925.5, 11455.5, 15970.5, 18525.5 kHz|||
|KWS78||Athens, Greece||  |
A typical CW marker sent by stations in this net was:
QRA QRA QRA DE KWS78 KWS78 KWS78 QSX 3/4/7/10/14 K
Besides the numerous CW and RTTY transmissions of the main players, sometimes also other callsigns were logged. Several publications have listed a larger number of stations, stating that they were part of this network too. Ary Boender has made a compilation of all the callsigns that were mentioned, in the following list.
- KKN32 Washington, DC, USA
- KKN35 Washington, DC, USA
- KKN39 Miami (possibly beamed to Central and S. America)
- KKN40 Monrovia, Liberia
- KKN44 Monrovia, Liberia
- KKN46 (Possibly beamed to Central and S. America)
- KKN50 Department of State, Washington, DC, USA
- KKN51 Washington, DC, USA
- KKN52 Washington, DC, USA
- KLA24 La Paz, Bolivia
- KRH50 Croughton, UK
- KRH51 Croughton, UK (c/s was logged on 2 freqs on 29-10-2000)
- KWK50 Tehran, Iran
- KWK95 Cairo, Egypt
- KWK97 Warsaw, Poland
- KWL90 Clark AFB, Philippines
- KWR86 La Paz, Bolivia
- KWS78 Athens, Greece (or Nicosia, Cyprus)
- 9GV Accra, Ghana
- Harry L. Helms, W5HLH: "How to tune the secret shortwave spectrum", Tab Books Inc, Blue Ridge Summit, PA, ISBN 0-8306-1185-1, pp. 57-60, 1981.
- Logs from the period 1989-1997 as published by WUN, SPEEDX, Popular Communications, Monitoring Times, DX-Antwerp, and the Utility Newsletter
- Bob Grove's Shortwave Directory, edited by Larry van Horn, N5FPW
- Michiel Schaay: "Embassy Radio Communications Handbook", Universal Electronics, Inc., Columbus, OH, ISBN 90-71915-10-7, pp. 51-52, 1988
- Tom Kneitel, W4XAA (ex-K2AES): "Guide to Embassy & Espionage Communications", CRB Research, ISBN 0939780062, 1986
- Donald W. Schimmel: "The Underground Frequency Guide", 3rd ed., HighText Publications, Inc., Solana Beach, CA, ISBN 1-878707-17-5, pp.88-95, 1994.
- Ary Boender: "KKN M25 Flashback", Numbers and Oddities, Issue 37, August 2001.
- BCLworld recordings
- Chris Smolinski: "KKN50 U.S. State Department", 1999
- Michiel Schaay: "Embassy Radio Communications Handbook", Universal Electronics, Inc, ISBN 90-71915-10-7, pages 51-52, 1988.