LONGBOW

LONGBOW was an early 20th century counterpart of the Unified Intelligence Taskforce. This world security organisation was set up by the UN precursor, the League of Nations. LONGBOW dealt with the occasional extraterrestrial incident, but was disbanded after it, and the League, failed to prevent World War II. (PROSE: Just War)

Roz Forrester knew that LONGBOW were familiar with the Doctor. (PROSE: Christmas on a Rational Planet)

The Home-Army Fifth Operational Corps reused Dolerite Base, an old LONGBOW facility beneath Edinburgh Castle. (PROSE: Moon Blink)

Behind the scenes
When asked on rec.arts.drwho what LONGBOW stood for, Just War author Lance Parkin admitted he only came up with "League of Nations Global..." He accepted Chris Schumacher's guess of "League Of Nations Global Bizarre Occurences [sic] Watch" as the "right answer".