Complex sentence: In mid May 1940, he was promoted captain and transferred to Luftwaffe's parachute arm, where he joined the 3rd Fallschirmjäger Regiment as a company commanders.
Split into simpler sentences: In mid May 1940, he was promoted captain and at the same time transferred to Luftwaffe and its parachute arm. Here he joined the 3rd Fallschirmjäger Regiment as one of its company commanders.