Fifth Column was the name MI5, the British Security Service, gave to a World War II operation run from 1942 until at least 1947. It was initially intended to identify people who would be willing to assist Germany in the event of an invasion of the United Kingdom, but as it developed, it also acted to divert its targets away from harmful activities. Although it ended up providing information on more than 500 suspects, it was the source of conflict within MI5, and after the war ended it remained secret, with none of the targets ever aware that they had been its subject. It was revealed in a release of files to the National Archives in 2014.