Complex sentence: After being put under British command the "O 16" took active part in WWII and sank three Japanese troopships and damaged two others, 4 of these troopships were attacked simultaneously on 12 December 1941 in the Gulf of Siam.
Split into simpler sentences: After being put under British command the "O 16" took active part in WWII. Later the O 16' sank three Japanese troopships and damaged two others, 4 of these troopships were attacked simultaneously on 12 December 1941 in the Gulf of Siam.