Harbour Defence Motor Launch

The harbour defence motor launch (HDML) was a British small motor vessel of the Second World War.

The HDML was designed by W J Holt at the Admiralty in early 1939. During the war, 464 HDMLs were constructed, mainly by yacht builders, in the United Kingdom and a number of other allied countries. In view of their later expanded combat roles in some Commonwealth navies some HDMLs were re-designated as "seaward defence motor launches" (SDML) or "seaward defence boats" (SDB).