XU XU ( X for " unknown " and U for " undercover agent " ) was a clandestine intelligence organisation working on behalf of Allied powers in occupied Norway during World War II . Though its work proved invaluable for operations against German operations in Norway , most of its operations , organization , etc . , were kept secret until 1988 . The name of the organization may have derived from Lauritz Sand , one of the founding members , who had previously worked for British intelligence in Dutch India and coined the name XU , X for « unknown » and U for « undercover agent » for his group . During the early stages of the German occupation of Norway , Sand collaborated with an intelligence group led by major John Hagle and captain Eivind Hjelle . By July 1940 , this group came into contact with another group led by Arvid Storsveen who had been a troop leader for a sabotage group in southern Norway . Although XU was initially organized by a leadership with a military background , its further development relied heavily upon recruiting students from the University of Oslo . As it grew , the group also included professionals around Norway , within railroads , police and so on , and collected maps and photos of German fortifications and forces . XU was initially organised as part of the Milorg , but as the Norwegian resistance movement grew , it became essential to compartmentalise organisations and teams and thereby enhance security against Nazi and Quisling infiltration , so XU split from the Milorg in the autumn of 1941 when Lauritz Sand and many others were arrested by the Gestapo . Milorg was the Norwegian counterpart to the sabotage service , the Special Operations Executive and so answered to Department FO . IV of the Norwegian High Command . From 1941 , XU answered to Department FO . II , which was the branch that worked with Britain ' s intelligence service SIS . In the spring of 1942 , the Gestapo became aware of XU ' s activities and initiated operations to identify and arrest its leaders . Several leaders from the Oslo cell , including Storsveen , fled to neutral Sweden in July 1942 , and set up headquarters for the organization there . They continued to move in and out of Norway , and Storsveen was killed in a Gestapo operation in Oslo in April 1943 without revealing his role in XU . XU continued its work under the leadership of Øistein Strømnæs and Anne - Sofie Østvedt , whose identities were kept secret until recently . Strømnæs led XU from occupied Oslo for the rest of the war . Apart from supplying the allied forces with very detailed data about the state of German forces in Norway , XU also had connections within Nazi Germany . Several of their members were couriers for MI5 agent Paul Rosbaud who had vital information regarding German nuclear research . By the end of the war XU had some 1 , 500 agents all over Norway and had developed a sophisticated courier system to the UK through neutral Sweden . The amount of information could amount to some 500 A4 pages supplied every day . The highly accurate and current intelligence enabled the Allied forces to maintain detailed information about the deployment and condition of German forces throughout Norway . This information proved vital in strategic bombing raids and would have been invaluable if an invasion had been necessary . XU maintained strict discipline around its cell structure , and the courier system was based on anonymous transfer of information . In one case , it turned out that two operatives who only knew each other by each other ' s shoes were close friends outside the XU network . After the war ended , confiscated Gestapo information revealed that the Gestapo in Norway had very little intelligence on the size , scope , members , and operations of XU . The existence of XU was not revealed to the general public until around 1980 , when the Norwegian government decided to decorate some of the XU members . The government was criticized for waiting for so long , especially since many double agents , otherwise sworn to secrecy , were convicted as collaborators during the post - war treason trials . Their names were cleared after 1980 , and as of 2006 , nearly all documents regarding the XU have been released to the public .