PRISM

PRISM was a global military organisation that replaced the United Nations Intelligence Taskforce, and later reformed as SILHOET.

History
It was created shortly before 2066, at a time of global stability, wealth, and confidence - this showed in its flying HQ SKYHOME, a "white elephant" secret base that gave itself away with its contrails until PRISM techs could figure out a solution.

It fought the Myloki from 2066-68. The Myloki could possess or replicate people and used this to fight a campaign of sabotage, which PRISM countered in secret. While the organisation won, the UN banking system collapsed as PRISM had needed to blow its budget.

In 2070, the organisation was exposed in the memoir Message is Clear and subsequently shut down. Commander Hal Bishop took the remnants of it underground as SILOET, using what remained of PRISM's resources and the fallen UN's funding. The shaky cover for their headquarters, the old BBC Television Centre, was that they were Britain's publicly funded film and TV company, the BFTV; this cover meant SILHOET was constantly being sent CVs and pitches by creators that they had to spend time faking meetings for. Despite the attempt at secrecy, various groups were aware SILHOET existed and where they were based.

When the Second Doctor appeared in 2096, SILHOET assumed he was a Myloki agent and panicked that it would be impossible to fight the aliens with the far meagre resources they had compared to last time. (PROSE: The Indestructible Man)

Behind the scenes

 * PRISM was based on SPECTRUM from the franchise, Captain Scarlet. SILOET was inspired by SHADO from the series (who used a film company as their cover).