HMS R4: The Submarine Nicknamed 'The Slug'

The Build: Chatham

HMS R4 was built at Chatham Dockyard, launched on 8 June 1918 and commissioned on 23 August 1919, one of ten R-class submarines, an unusual and ambitious design conceived specifically as a hunter-killer submarine, prioritising submerged performance over surface speed at a time when most submarines were built the other way around.

She displaced 410 tons surfaced, armed with six 18-inch torpedo tubes and fitted with five hydrophones for detecting enemy submarines underwater.

The First Submarine Built the Right Way Round

Those figures deserve to be set against each other, because they are the most interesting numbers in early submarine design. On the surface R4 could manage nine and a half knots, driven by a single diesel engine of 240 brake horsepower. Dived, she could do fifteen, driven by two electric motors drawing on two hundred and twenty battery cells and developing something like 1,200 horsepower.

Read that again. She had five times as much power available underwater as she had on the surface, and she was substantially faster dived than surfaced. No submarine had ever been built that way before. Every other boat of the period was a surface torpedo craft that could submerge to hide or to attack, with a big engine for getting places and a small battery for the sprint at the end. The R class inverted the whole thing.

They did it by making everything else worse on purpose. The hull was shaped for water rather than for weather, which is why she looked like a slug and handled like one on the surface. There was one screw instead of two. There was no deck gun. The single small diesel meant a wretched surface passage and a long wait to charge. All of that was accepted in exchange for fifteen knots underwater, because underwater was where the enemy was.

It is worth being clear how far ahead of everybody this was. Nothing else in any navy was built to be faster dived than surfaced until the German Type XXI in 1944, twenty-six years later, and that boat is usually described as the design that changed submarine warfare forever. The Royal Navy got there first, in 1918, and then quietly forgot about it. She was also the first British submarine with six 18-inch bow tubes, and she was designed to go to 250 feet, though in service she was held to 150.

Arriving Too Late

Like most of her sister R-class boats, R4 came too late to see any combat in the First World War, commissioning only after the armistice had already been signed, an all too familiar story for submarines rushed into an ambitious wartime building programme that simply could not keep pace with events.

The class did get one shot in, though not R4, who was still being finished. Operating out of Killybegs in County Donegal in October 1918, an R-boat picked up a U-boat, tracked her, and fired a full salvo of all six tubes. One torpedo hit. It did not go off.

That dud is one of the better near-misses in naval history. Had it detonated it would have been the first time in the world that one submarine sank another, and it would have been done by a boat purpose-built for the job, twenty-seven years before HMS Venturer finally managed it against a submerged target in 1945. Instead the R class went into the record with nothing at all, and the first sinking of a submarine by a submarine went to boats that had never been designed for it, catching their victims on the surface, as HMS Telemachus did.

The awkward truth is that the concept could not have worked in 1918 whatever the torpedo did. Two things were missing. First, the five hydrophones could only hear anything while the boat was going slowly and quietly, so she had to choose between listening and using the fifteen knots that were her entire reason for existing. Second, and worse, there was no way on earth to aim at a target you could only hear. A hydrophone gives a rough bearing and nothing else: no range, no depth, no course.

So the R class had the right idea and none of the equipment. Everything needed to make it work, active sonar, a fire control system that could solve for a target in three dimensions, homing torpedoes and an engine that did not need air, arrived over the following forty years. When they did, the result was HMS Dreadnought and every hunter-killer since, which is this design finally given the tools to do its job.

A Distinctive Shape and a Grounding

R4 earned the affectionate nickname 'The Slug' from her crews, on account of her distinctive hull shape, and ran aground at Exmouth on 1 November 1926, though she was refloated ten and a half hours later without lasting harm. She spent much of her remaining service as a training target at the Portland anti-submarine school, valuable if unglamorous work helping to train the Navy's escort crews in submarine detection.

There is a neatness to that ending which is usually missed. R4 was built to hunt submarines by listening for them, and she could not, because the listening gear of 1918 was not good enough. She then spent the last decade of her life at Portland being listened for, so that the Royal Navy could work out how to do it properly. The boat the concept defeated became the training aid that helped fix it.

It was not a token job either. The anti-submarine school at Portland was where Asdic was developed into something usable, and developing it required a real submarine, dived, doing unhelpful things. The escort crews who worked the Atlantic in the next war learned their trade in a system built partly on afternoons spent chasing a slow slug-shaped boat around Portland Harbour.

The End of Her Service

HMS R4 was sold on 26 May 1934 to Young of Sunderland for scrap, the only one of her class still afloat by then, bringing to a close the career of a submarine whose ambitious design had, in the end, found her most useful role not hunting enemy submarines but helping to train the sailors who would one day hunt them.

She outlasted every one of her sisters by a decade, which for a boat of a class written off as a failure is a fair innings. Most of the R boats were gone by 1923, sold within five years of commissioning because nobody could think what to do with a submarine that was useless on the surface. R4 survived because being awkward on top and quick underneath is precisely what you want in a training target.

The design was right and the century was wrong. Everything the R class was reaching for, a fast, quiet boat built for the water rather than the weather, whose job is other submarines, is a plain description of every attack submarine now in service, and the line runs through the diesel boats like HMS Oberon to the nuclear ones. She was scrapped at Sunderland in 1934, sixteen years old, having been a good idea about thirty years early.