Destroyer HNLMS Isaac Sweers, as completed, underway, coastal waters (1941). (Imperial War Museum FL 14111) HNLMS Isaac Sweers was one of four Gerard Callenburgh-class destroyer built for the Royal Netherlands Navy during World War II. Design and Construction The keel was laid on 26 November 1938. The ship was launched on 16 March 1940 and the unfinished ship was evacuated to England after the German invasion of the Netherlands. She was completed in Great Britain, with six British 4-inch dual purpose guns instead of planned five 120 mm guns. The ship was modern for her time, she was fast and had two manually stabilized 40 mm Bofors AA guns, each with its own Hazemeyer fire control, an on-mount mechanical analog fire control computer integrated with a on-mount optical rangefinder. It was the first Dutch ship to use a Dutch radio direction finder (RDF 289), to aim its AA guns. The ship's plans were saved from the Germans and elements were incorporated into Royal Navy ship desi...