Complex sentence: After the United States Army Corps of Engineers took over the Manhattan Project in August 1942, the Manhattan District initially coordinated the work, but assumed responsibility for the Metallurgical Laboratory contract on 1 May 1943.
Split into simpler sentences: After the United States Army Corps of Engineers took over in August 1942, the Manhattan District coordinated the work. It assumed full responsibility for the Metallurgical Laboratory contract on 1 May 1943.