Complex sentence: The 229th Engineer Company ultimately becomes part of a 30,000-man Amphibious Training Force 9 (ATF-9), whose mission is to recapture the Aleutian Island of Kiska, occupied by Japanese troops.
Split into simpler sentences: The 229th Engineer Company ultimately becomes part of a 30,000-man Amphibious Training Force 9 (ATF-9). Their mission was to recapture the Aleutian Island of Kiska, occupied by Japanese troops.