'Bittern' was a British operation by the Special Operations Executive to train Norwegian resistance groups in assassination operations, assist in the carrying out of assassinations, and help prisoners to escape from German-occupied Norway (October/December 1942).
Preparations began in June to train two Norwegians, including Johannes Andersen, to undertake assassinations. In March Andersen had killed Raymond Colberg, an Abwehr agent, and his criminal background attracted him to SOE. The four-man 'Bittern' party (Jan Allen, Rubin Larsen, Erik Aasheim and Andersen) was parachuted into Norway during the night of 3/4 October with a list of informers. For security reasons the real nature of the undertaking was not communicated to the Norwegian resistance, and as a result of this, confusion over its role and the behaviour of the party’s most notorious member, the undertaking ended without having carried out its primary task. By the end of the year the whole team had escaped to Stockholm in neutral Sweden.