J-class Submarine - Design

Design

Shortly before the First World War, incorrect reports reached the British fleet that the Germans were planning a class of fast submarines for operation with the fleet, and British efforts turned toward provision of similar vessels. The driving requirement would be a surface speed that matched the speed of the battlefleet. In order to meet the requirement, the DNC designed a three shaft submarine that was 100-foot (30 m) longer than the E-class, with electric motors confined to the two outer shafts and a hull form based on a light cruiser. This resulted in a diesel-electric design that was unique within the Royal Navy.

The power requirement was 1200 horsepower per diesel engine. In order to meet this power requirement, Vickers, the pre eminent builder of submarine diesels in World War I Britain, elected to produce a 12-cylinder version of their previously successful 100 brake horsepower per cylinder six- and eight- cylinder engines for the D and E classes respectively. They retained the 14.5-by-15-inch (370 by 380 mm) bore and stroke of these previous engines and produced 1200 shaft horsepower at 380 revolutions per minute. These engines eventually went into the J, L-class and M-class submarines.

The design featured four bow tubes and two beam tubes for 18-inch torpedoes; they were the first British submarines to carry four bow tubes. Although designed to reach 19.5 knots (36 km/h), the boats could only practically travel at 19 knots (35 km/h), making them too slow for fleet use. The quest for fleet submarine performance turned toward the subsequent, steam powered K-class. The endurance of the J class was considerably greater than previous submarines.

Eight boats were originally ordered, although two were later cancelled, while a seventh was later reordered to a slightly modified design. The first six were laid down between March and May 1915, with J7 laid down in August 1916. The six early boats were completed between April and August 1916, and J7 in November 1917.