sentences:  From 1944 the Fortress IIs and IIIs were being used by the specialist electronic countermeasures squadrons of No.100 Group RAF
  
  USAAC / USAAF was main operator of all versions of the Boeing B-17 Flying Fortress.Most units operating B-17 were based in the European Theatre of World War II but aircraft was used at some point in all theatres of World War II.