The harbour defence companies were responsible for local defence and for the security of the ships and submarines moored in the harbour. These companies and the harbour defence boats used to patrol the river were under the command of Harbour Commander "Korvettenkapitän" Kellerman. The 333rd Infantry Division was the German Army unit responsible for the defence of the coast between St Nazaire and Lorient. The division had no troops based in the town, but some were located in villages nearby and would be able to respond to any attack on the port.