Complex sentence: Lütjens received the a prompt award of the Clasp to the Iron Cross 2nd Class (1939) three days later and conducted Destroyer operations in the North Sea over the winter, 1939--40, which earned him the Clasp to the Iron Cross 1st Class.
Split into simpler sentences: Lütjens received the a prompt award of the Clasp to the Iron Cross 2nd Class (1939) three days later. His command of Destroyer operations in the North Sea over the winter, 1939--40, earned him the Clasp to the Iron Cross 1st Class.