ABSTRACT
The U-boat of the First World War relied on surface travel for tactical mobility and for searching for its targets, where using their diesel engines they could achieve 18½ knots in good conditions. They would submerge when threatened by antisubmarine (A/S) forces or, sometimes, in rough weather. Once underwater, the Uboats relied on their batteries and electric motors for propulsion, which gave them a top speed of about eight and a half to nine and a half knots but only for an hour. At, say three and a half knots, however, the U-boat’s underwater endurance was about 24 hours. Charging the batteries could only be done on the surface when the diesel engines could be run, so these boats were in every sense ‘submersibles’.1
