The HDML was a 72-foot Admiralty design with a modest top speed but a range of about 2,000 nautical miles at economical speed. Its typical armament of 20 mm cannon, machine guns, and depth charges made it a practical anti-submarine and patrol craft rather than a high-speed attacker. The double-diagonal wooden hull was divided into six watertight compartments, giving the boat useful resilience after flooding. Tropical boats could also receive copper sheathing against marine borers, while wartime timber shortages led builders to substitute larch for mahogany. The 486 completed boats included American-built examples associated with Lend-Lease, and some later served with the Royal Netherlands Navy. The example prepared for a Malta passage illustrates how the Royal Navy used an unglamorous craft across very large operational spaces.
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Harbour defence launches with oceanic reach
The modestly named Harbour Defence Motor Launch was a long-range, wooden anti-submarine craft whose practical service reached far beyond a literal harbour.