Operation Regenbogen and the order to destroy the U-boats

Operation Regenbogen was intended to deny German submarine technology and intelligence to the Allies. By April and May 1945, British intelligence already had extensive access to German information, with similar penetration suspected for the American and Soviet services. Boats in harbour could be scuttled with some prospect of crew survival. Crews at sea were also expected to destroy their boats, preferably after reaching neutral waters. Scuttling in the open Atlantic meant abandoning the submarine for a wartime life raft with poor prospects of reaching shore.