Complex sentence: Until December 2011, he was the Deputy Chief of Mission of the U.S. Embassy in Tokyo, Japan where he also served as chargé d'affaires ad interim during the absence of the Ambassador from January 15,2009 till August 20,2009.
Split into simpler sentences: Until December 2011, he was the Deputy Chief of Mission of the US Embassy in Tokyo, Japan. He had been the chargé d'affaires ad interim during the absence of the Ambassador from January 15,2009 till August 20,2009.