Complex sentence: The attack started at 21; 00 hours 11 December, Halser and Sparks in "Catfish" attacking shipping on the western side of the dock, placed eight limpet mines on four vessels including the fast patrol boat Sperrbrecher.
Split into simpler sentences: The attack started at 21; 00 hours 11 December, Halser and Sparks in "Catfish" would attack shipping on the western side of the dock. They placed eight limpet mines on four vessels including the fast patrol boat Sperrbrecher.