HMS B4: An Early B-Class Boat That Guarded the Dover Straits

The Build: Barrow-in-Furness

HMS B4 was built at the Vickers shipyard in Barrow-in-Furness, launched on 14 November 1905 and commissioned on 28 January 1906, one of eleven B-class submarines built for the Royal Navy in the first decade of the twentieth century, small early boats displacing just 287 tons on the surface and 316 tons submerged, armed with two 18-inch torpedo tubes in the bow, crewed by only two officers and thirteen ratings.

Fifteen men in two hundred and eighty-seven tons is the figure to start from, because nothing else about her makes sense until you have it. A B class boat was a hundred and forty feet of steel tube with no internal bulkheads at all: one continuous space from the torpedo tubes to the motors, containing the batteries, the engine, the torpedoes, the controls and everybody aboard. There was no separate engine room because there was no room to separate.

She ran on petrol. Not diesel, which the Royal Navy did not adopt until later, but petrol, and the exhaust from a petrol engine in an unventilated steel tube goes exactly where the crew are. There was ventilation fitted for the batteries, which produced hydrogen and would explode if it accumulated, and none at all for the living space. So these boats carried mice. A mouse is small enough that carbon monoxide affects it well before it affects a man, and a quiet cage was a warning that everybody had a few minutes to do something about it. That is not a colourful anecdote. It was the carbon monoxide detector.

The reason the Admiralty tolerated all this is that nobody had a better answer yet, and the cost of finding out was paid by the class before hers. The A boats, from which the Bs were directly developed, were catastrophically dangerous: A1 suffered the first explosion in any submarine, from a pocket of hydrogen, before she had even been delivered, and in 1904 she became the first submarine the Royal Navy ever lost, going down with every man aboard. One of them had to be abandoned off Land's End when seawater reached the batteries and filled her with chlorine. Almost every boat of that class had an accident of some kind and several of them were fatal.

The B class was the improvement. She had proper hydroplanes forward, a real conning tower and bridge you could stand on, and considerably greater endurance than an A boat. Judged against anything afloat twenty years later she was a death trap, and judged against what came immediately before her she was a considerable step towards not being one. The Royal Navy went on learning that lesson expensively for another two decades: HMS K3 is what the same impatience produced in 1917.

An Early Collision

Just months into her career, B4 collided with a dredger while entering Portsmouth harbour on 21 July 1906, suffering significant damage that required repairs in dry dock, an early reminder of just how hazardous even routine harbour manoeuvres could be for these primitive early submarines.

The harbour part is not incidental. A submarine of 1906 on the surface sat very low, showed almost nothing above water, had no bridge worth the name in the modern sense and steered from a hatch. She was, in a crowded working harbour full of dredgers and lighters and picket boats, close to invisible and largely unable to get out of anybody's way. Most of the damage done to early British submarines was done within sight of land by other British vessels, and it went on being true for a long time afterwards.

Guarding the Straits of Dover

When war broke out in 1914, B4 was assigned to help defend the Straits of Dover, one of the most strategically vital and heavily trafficked stretches of water in the entire war, essential to keeping the English Channel closed to German shipping and submarines throughout the conflict.

Her part in it was more modest than that suggests, and the record is quite specific. In 1914 and 1915 she belonged to the Harbour Defence Flotilla at Dover, commanded by Lieutenant Commander A. C. R. Bennett with Lieutenant Chisholm as his second. Harbour defence is exactly what it sounds like. By 1914 a nine-year-old B boat could make about twelve knots on the surface and very little dived, carried two torpedoes with no reloads and no gun at all, and had a radius of action measured in tens of miles rather than hundreds. She could not hunt anything. What she could do was lie off the entrance to a harbour or a strait and wait, which in the Dover Straits in 1914 was a genuinely useful thing to be doing, because the whole British strategy in the Channel rested on making the passage look expensive.

She was also part of something new. A photograph of her from 1914 survives, captioned as showing her wireless telegraph installation, and putting W/T into boats of this size changed what they were for. A submarine that cannot communicate can only attack what swims past her. A submarine that can report becomes a pair of eyes at the end of a wire, able to tell an admiral what is moving through a strait while remaining where she is. Almost everything submarines have done since has depended on that, and it was being bolted onto nine-year-old petrol boats in 1914.

In 1915 and 1916 she was at Ardrossan, on the Ayrshire coast, which is about as far from the fighting as a British submarine could be posted. The B boats were already obsolete when the war started and were finished as fighting units well before it ended.

Surviving the War

HMS B4 survived the First World War intact, a genuine achievement for a submarine of her vintage and design, before being sold for breaking up on 1 April 1919 to the Ardrossan Dry Dock Company, bringing to a close the career of one of the Navy's earliest and hardiest little submarines.

What Happened to the Others

Six of the eleven went to the Mediterranean and had a much louder war than she did. HMS B6 carries that story: Gallipoli, the Dardanelles, and the extraordinary second life the survivors were given. By the autumn of 1915 those boats could not be kept running for lack of spare parts and were sitting idle, so rather than waste them the Admiralty came to an arrangement with the Italian navy and had them rebuilt at Venice in 1917 as surface patrol boats, with the conning tower replaced by a raised wheelhouse and a 12-pounder gun on the casing. They were renumbered into an S series and sent to patrol the Otranto Barrage. They were not reliable, and before long they were back at Malta being paid off.

B4 did none of that. She stayed in home waters, kept her conning tower and her petrol engine, and was still afloat and in one piece at the Armistice. She was sold in 1919 to the Ardrossan Dry Dock Company, which is the same Ardrossan she had been stationed at three years earlier, so she ended up being broken up in a place she already knew.

Calling that survival a genuine achievement is not sentiment. Of the boats built alongside and immediately before her, a great many killed their own crews without an enemy anywhere near, and the men who went to sea in them did it knowing that. B4 spent fourteen years running a petrol engine in a steel tube with no bulkheads and fifteen people and a cage of mice, and there is no record of her ever losing a man. There are worse things for a warship to have on her record than nothing at all.