'Unke-Nikolaus' was a German undertaking to create and deploy covert special forces teams in Budapest, the capital of Hungary, during and after its capture by the Soviets (December 1944/about February 1945).
In the battle for Budapest between 29 December 1944 and 13 February 1945, as part of the Soviet 'Budapest Strategic Offensive Operation', Adolf Hitler declared the Hungarian capital to be a fortress to be held or, if lost, to be recaptured at all costs. The Oberkommando des Heeres knew that this was an impossibility, but as a sop ordered the organisation of the so-called Frontaufklärungskommando 206 as a covert special forces unit. This was to comprise specially recruited local special forces who were to remain in Budapest in 'Unke' as supposed residents and then undertake espionage and sabotage activities against the Soviet forces and administration. They were also to discover and report the movements of Soviet formations, and provide safe houses. The German officers tasked with establishing liaison with the 'residents' were to be infiltrated into the city by land or dropped by parachute.
To further the work of the 'resident' parties, at 19 locations within the city some 37 disguised packages of explosives and at five other locations packages of fuses and detonators were hidden in 'Nikolaus'. The plan was for 'resident' parties to use these to sabotage the transport infrastructure and demolish public buildings.
Whether or not the operation was carried out, and if the former how successful it was, remain unknown.