Unternehmen Donnerkeil (Operation or Undertaking Thunderbolt) was the codename for a German military operation of the Second World War. Donnerkeil was designed as an air superiority operation to support the Kriegsmarine‍‍ '​‍s (German Navy) Operation Cerberus, also known as the "Channel Dash".In 1941 Kriegsmarine surface vessels had carried out commerce raiding sorties in support of the German U-Boats in the Battle of the Atlantic.