HMS B4 was one of 11 B-class submarines built for the Royal Navy in the first decade of the 20th century. The boat survived the First World War and was sold for scrap in 1919.
The B class was an enlarged and improved version of the preceding A class. The submarines had a length of 142feet overall, a beam of 12feet and a mean draft of 11feet. They displaced 287LT on the surface and 316LT submerged. The B-class submarines had a crew of two officers and thirteen ratings.[1]
For surface running, the boats were powered by a single 16-cylinder 6000NaN0 Vickers petrol engine that drove one propeller shaft. When submerged the propeller was driven by a 180hp electric motor. They could reach 12kn on the surface and underwater.[1] On the surface, the B class had a range of 1000nmi at .[2]
The boats were armed with two 18-inch (450 mm) torpedo tubes in the bow. They could carry a pair of reload torpedoes, but generally did not as they would have to remove an equal weight of fuel in compensation.[3]
B4 was built by Vickers at their Barrow-in-Furness shipyard, launched on 14 November 1905 and completed on 28 January 1906.[4]
B4 collided with a dredger when entering Portsmouth harbour on 21 July 1906 and was badly damaged as a result, having to be beached before being taken into dry dock for repair.[5] When the war began in 1914, the boat was assigned to defend the Straits of Dover. B4 was sold for breaking up on 1 April 1919 to the Ardrossan Dry Dock Co.