Telemark is a map in Battlefield 1942: Secret Weapons of WWII. The target is a nuclear reactor that the Germans are using as heavy water in order to create a world-first atomic bomb to destroy an Allied target of their own. The SAS won a remarkable victory in preventing the bomb to be made.
This is the primary target for the SAS and headquarters of German Admiral, Karl Donitz. The Wehrmacht uses vehicles and/or tanks to defeat the commando team that's going to destroy them and Donitz creates a world-first atomic bomb inside the facility. If Germany wins, they create the bomb and choose a target of their own but if the United Kingdom wins, the Germans lose their chance on creating this new weapon.
Sir Charles Hambro uses everything from tanks to soldiers in this battle to rid the Germans of creating an atomic bomb and defeat the German army there. If Germany captures this, their weapon is created and used to defeat the British by bombing one target of their own choice and where they will do it.