In 1802, intending to make Cherbourg one of his main military ports in preparation for his invasion of the United Kingdom, Napoleon I ordered that work on the harbour wall be resumed to La Bretonnière's plans, by building up the central section to mount cannon. A decree of 25 germinal year XI (1803) ordered the engineer Cachin to excavate the military outer harbour at lac de Moeris - this was opened on 27 August 1813 in the presence of empress Marie-Louise of Austria. That decree also ordered the construction of a new arsenal at the port. 1803 also saw Cherbourg's harbour fend off British attacks and become a base for privateers.