Complex sentence: Clayton remained with Basie until he was called up for war service in November 1943, and being based at Camp Kilmer near New York, he was able to participate in various all-star sessions, some of which were led by Sy Oliver.
Split into simpler sentences: Clayton remained with Basie until he was drafted for war service in November 1943. Based at Camp Kilmer near New York, Clayton was able to participate in various all-star sessions, some of which were led by Sy Oliver.