HMS Sidon (P259): A Peacetime Tragedy at Portland

Constructed at Birkenhead, Serving Through the War's Final Months

HMS Sidon was built by Cammell Laird at Birkenhead, laid down in July 1943, launched in September 1944 and commissioned that November, an Improved S-class submarine that deployed to the Far East in the spring of 1945, reaching Trincomalee that May and going on to rescue a downed American airman during a war patrol in the south west Pacific before Japan's surrender brought the fighting to a close.

She was present for the reoccupation of Hong Kong before returning home to be paid off at the very end of that year.

A Decade of Ordinary Peacetime Service

Recommissioned for peacetime service, Sidon underwent a series of refits and modernisations through the late 1940s and early 1950s, including the fitting of a snorkel mast and radar, and took her place among the fleet at the Coronation Review of 1953. There was nothing in this decade of routine service to suggest the tragedy that awaited her.

That is worth dwelling on for a moment, because it is the ordinary condition of a submarine in peacetime and it is where most of them spent most of their lives. Refits, workups, exercises, a fleet review, and then more exercises. HMS Scorcher had almost exactly the same decade. The overwhelming majority of the men who served in these boats went to sea, did the job, and came home again for years on end with nothing whatever to report.

The exception, when it comes, does not usually come from the enemy. It comes from the boat.

The Explosion

On the morning of 16 June 1955, moored alongside her depot ship HMS Maidstone at Portland, Sidon was preparing to load a new type of experimental torpedo for forthcoming trials, a high test peroxide fuelled weapon known as the Fancy, or Mark 12.

At around 8.25am, an explosion tore through a torpedo loaded in the number three tube, the result, investigators later concluded, of the weapon's starting mechanism being accidentally engaged while it remained enclosed inside the tube, causing its volatile fuel system to rupture.

What High Test Peroxide Is, and Why It Did That

The substance at the centre of this deserves explaining, because everything that happened follows from its chemistry. High Test Peroxide is hydrogen peroxide at very high concentration, around eighty-five per cent or more, which is a very long way from the bottle in a bathroom cabinet.

At that strength it is not really a fuel, it is an oxidiser waiting for an excuse. Hydrogen peroxide wants to decompose into water and oxygen, and it does so violently in the presence of a catalyst. The catalyst can be almost anything: rust, dirt, an organic contaminant, a trace of the wrong metal. The decomposition releases a great deal of heat very quickly, the water flashes to steam, and the volume increase is enormous. The attraction of it in a torpedo was that it carries its own oxygen, so an engine can burn fuel with it underwater and produce far more power and far higher speeds than an electric motor. The Germans developed the idea during the war and the British and Soviet navies both took it up afterwards.

What happened in number three tube is now well documented. The torpedo hot ran, which is the submariner's term for a weapon whose engine starts while it is still aboard. In the water a propeller has something to push against; inside a tube it has nothing, so the engine over-sped violently. An oxidiser line burst and sprayed HTP over the copper components inside the weapon. Copper is one of the things that catalyses HTP most efficiently. The result was a steam explosion.

That is why the inquiry blamed the design rather than the crew. Nobody aboard did anything wrong. They had loaded a weapon that could destroy itself if a single line failed, and they had been given no reason to think so.

The resulting chemical reaction and fire breached two watertight bulkheads, filling the forward part of the boat with flame and toxic fumes that killed most of the men in that section almost instantly. Sidon sank by the bow at 8.45am, roughly twenty minutes after the initial blast, settling in shallow water while still tied up alongside.

The circumstances make it worse rather than better, and it is worth saying why. Sidon was in a defended harbour, in daylight, secured to her depot ship, with a fully equipped medical department, fire parties, cranes, divers and hundreds of trained men within a few yards of her. Every advantage a submarine in trouble could possibly have, she had.

And it made almost no difference, because the men in the forward compartments were killed in the first seconds by blast, fire and fumes. There is no rescue that answers that. The most anybody alongside could do was go in after the ones who might still be alive, which is exactly what happened.

A Doctor Who Would Not Stop Trying

Thirteen men in total lost their lives. Twelve were killed in the immediate explosion and fire, and the thirteenth was Temporary Surgeon Lieutenant Charles Rhodes, the medical officer of HMS Maidstone, who repeatedly entered the smoke filled, flooding submarine to treat and rescue injured crewmen, ultimately dying himself after using an escape apparatus he had never been trained to operate.

The award he received deserves explaining, because the Albert Medal has largely been forgotten. It was instituted in 1866 for saving life at sea and later extended to land, and until 1940 it was the highest British award available for civilian gallantry. When the George Cross was created it took that place, and the Albert Medal was discontinued altogether in 1971, with surviving holders invited to exchange theirs for the George Cross.

Charles Rhodes was not a submariner. He was the depot ship's doctor, which means he had no business being inside a burning submarine at all and no training for the equipment he used to try to get out of one. He went in more than once. It is the sort of thing that is easy to describe and almost impossible to imagine doing: climbing down a hatch into a compartment filling with smoke and water, in a boat that is visibly sinking, because somebody down there might still be alive.

He was posthumously awarded the Albert Medal for gallantry in saving life at sea, a recognition that speaks to the genuine, selfless courage he showed in the accident's chaotic final minutes. Parliament was told on the day itself that a further eight men, one officer and seven ratings, had been injured and hospitalised, out of fifty six personnel aboard in total, meaning forty three survived.

It was a devastating loss of life in peacetime, in a harbour, in front of witnesses.

An Inquiry, and a Withdrawn Weapon

A formal court of inquiry, convened in the immediate aftermath, is reported to have cleared Sidon's own crew of any blame, attributing the disaster instead to a fundamental design fault in the experimental torpedo itself rather than any error by those aboard.

Further problems with the same high test peroxide torpedo programme surfaced again later that year, and the weapon was ultimately withdrawn from service before the end of the decade, a quiet but significant consequence of the tragedy at Portland.

The Same Accident, Forty-Five Years Later

It was a great deal more significant than quiet, and the reason is that another navy did not draw the same conclusion.

On 12 August 2000 the Russian nuclear submarine Kursk was on exercise in the Barents Sea. A practice torpedo in one of her tubes leaked high test peroxide. The leak found something to react with, the resulting explosion blew off both the inner and the outer doors of the tube, and the fire that followed destroyed the bulkhead between her first and second compartments. Roughly two minutes later the warheads of the other torpedoes in the compartment went off. All one hundred and eighteen men aboard died, some of them not immediately.

The official Russian investigation identified the leaking HTP torpedo as the cause. And the man who first put the two accidents side by side in public was Maurice Stradling, a former Royal Navy torpedo engineer who had worked on the British high test peroxide programme and recognised the pattern immediately.

The Royal Navy had thirteen dead in a harbour in 1955 and abandoned the technology within four years. The Soviet Union kept it, and the Russian Navy still had HTP torpedoes aboard in the year 2000. That is the whole of the story, and it is why the withdrawal of the Mark 12 belongs near the top of Sidon's record rather than at the bottom.

It is also worth saying that Britain drew the lesson because thirteen men died alongside a depot ship where everybody could see it. A submarine that had hot run at sea might simply have disappeared, and nobody would have known why.

A Wreck That Remains

Sidon was raised about a week after sinking but found to be damaged beyond economical repair, and was never returned to service.

She was deliberately sunk again two years later, in June 1957, to serve as a sonar training target off Portland, and her wreck remains there to this day, now a well known site for recreational divers exploring the waters off Weymouth, a quiet resting place for a submarine whose story is defined, in the end, not by any battle, but by a single, tragic accident in peacetime and the genuine courage shown in its aftermath.

That she ended as a sonar target is not disrespect, and it is worth explaining because it looks like it. She had been raised, her dead had been recovered and buried ashore, and the hull was damaged past economical repair. A submarine on the bottom in known water is genuinely useful to anti-submarine crews, who otherwise have to learn what a bottomed submarine sounds like from a textbook.

She sits in Weymouth Bay in water shallow enough to dive, upright and largely intact, and is one of the better-known wrecks on that coast. Divers who go down to her are looking at the boat, not at a grave: nobody is aboard.

Sidon belongs in a short and unhappy sequence. HMS Thunderbolt, as Thetis, went down on trials in Liverpool Bay in 1939 and taught the Royal Navy that men must be able to escape without help. HMS Truculent sank in the Thames in 1950 and taught that getting out is not enough if the tide is running. Sidon taught the third lesson, which is that the most dangerous thing aboard a submarine is very often the weapon she is carrying.