As a continental power intent on offensive operations, Germany could not ignore the need for aerial support of ground operations. Though the Luftwaffe, like its counterparts, tended to focus on strategic bombing, it was unique in its willingness to commit forces to CAS. Unlike the Allies, the Germans were not able to develop powerful strategic bombing capabilities, which implied industrial developments they were forbidden to take according to the Treaty of Versailles. In joint exercises with Sweden in 1934, the Germans were first exposed to dive-bombing, which permitted greater accuracy while making attack aircraft more difficult to track by antiaircraft gunners. As a result, Ernst Udet, chief of the Luftwaffe's development, initiated procurement of close support dive bombers on the model of the U.S. Navy's Curtiss Helldiver, resulting in the Henschel Hs 123, which was later replaced by the famous Junkers Ju 87 "Stuka". Experience in the Spanish Civil War lead to the creation of five ground-attack groups in 1938, four of which would be equipped with "Stukas". The Luftwaffe matched its material acquisitions with advances in the air-ground coordination. General Wolfram von Richthofen organized a limited number of air liaison detachments that were attached to ground units of the main effort. These detachments existed to pass requests from the ground to the air, and receive reconnaissance reports, but they were not trained to guide aircraft onto targets.