Hurd Deep, 16 April 1951: the loss of HMS Affray

On 14 November 1951, seven months after HMS Affray failed to surface in the English Channel, the First Lord of the Admiralty rose in the Commons to set out what the Royal Navy had concluded. J. P. L. Thomas had read the Final Report of the Board of Inquiry, dated 6 August 1951. He had read the metallurgical tests run on the only piece of Affray ever recovered, her broken snort mast. The Board’s best estimate, he said, was material failure of that mast. He then said, in terms, that he could not endorse it. “There is insufficient evidence,” he told the Commons, “to enable me to say with certainty why ‘Affray’ was lost.”

That is an unusual sentence for a First Lord to put on the record about a peacetime training submarine lost in home waters. The boat had been found. A Board had sat. A most likely cause had been identified. He could have read the conclusion into Hansard and moved on. He did not. He named a second possibility, a major battery explosion that ruptured the pressure trunking, as a live alternative the evidence could not rule out. He called the snort metallurgy “below standard” and the welding “not good,” and declined to say the mast had failed in service. The case has been raised in Parliament twice since, in 2007 and 2012. The Ministry of Defence has not revised its position.

This piece is the route the inquiry took to that admission, and the reason the broken mast on the seabed off Alderney still cannot, on its own, settle which failure killed her.

The documented account

HMS Affray, pennant P421, was an Amphion-class diesel-electric attack submarine. She was built at Cammell Laird in Birkenhead, laid down on 16 January 1944, launched on 12 April 1944, and commissioned on 25 November 1945. She was one of sixteen boats of her class, designed for long-range Pacific operations against Japan, and arrived too late for the war she had been built for. The standard secondary record summarises four years of postwar service with the British Pacific Fleet.

In March 1949 Affray was drydocked for the retrofit that would dominate her later record. A snort mast, the Royal Navy’s name for a snorkel, was fitted in January 1950. The snort is a pneumatically raised steel tube providing air induction and exhaust extraction so the boat can run her diesels at periscope depth. It gave trouble almost from fitment. A mechanic, William Day, is quoted in the secondary record describing the engine room as routinely flooded after snorting; the underlying source has not been confirmed here. A repair to a known battery tank leak was scheduled for after the exercise that killed her. She sailed on 16 April 1951 with the leak under planned, not completed, repair.

The exercise was Exercise Spring Train, a simulated war patrol. A four-man Special Boat Service detachment was to be put ashore on an isolated Cornish beach and extracted under cover of darkness. Her commanding officer, appointed in March 1951, was Lieutenant John Blackburn DSC, RN, working a new crew up to operational status.

Affray sailed from Portsmouth at approximately 1600 hours on 16 April 1951 with seventy-five men aboard, against a normal complement of sixty-one. She carried a reduced crew of fifty; the remaining twenty-five were passengers on the simulated patrol, including thirteen sub-lieutenants under training, seven engineering-branch lieutenants, an Engineer Commander, a naval instructor, and the four SBS Royal Marines.

At 2100 hours on 16 April, Affray made her last surface signal, reporting her position and her intention to dive at 2115 hours. The frigate HMS Contest was the last surface contact that evening. Affray failed to make her scheduled surfacing report at 0800 hours on 17 April. At 1100 hours the Admiralty declared Subsmash, the standing Royal Navy submarine search and rescue procedure. The search drew in twenty-four vessels from four nations, led by HMS Agincourt; the participating submarines flew white flags to distinguish themselves from the missing boat. Subsmash was cancelled at 1945 hours on 19 April, sixty-nine hours after Affray’s last dive.

A lower-intensity search continued. On 14 June 1951, HMS Loch Fyne made the initial asdic contact on the very edge of Hurd Deep, the steep-sided submarine trench north of the Channel Islands. HMS Reclaim, the Royal Navy’s deep-diving vessel, was sailed to the position and confirmed the identification using a newly fitted underwater television camera built for the Admiralty by Pye Ltd of Cambridge. The Imperial War Museum holds the 1952 film of the operation. The first thing the camera resolved on the hull was the lettering YARFFA, AFFRAY backwards across the steel. The wreck lay in approximately 86 metres of water, about 282 feet.

A Board of Inquiry under Rear-Admiral R. M. Dick had been convened during the search. Its interim finding, on 19 July 1951, identified material failure as the most likely class of cause, having considered battery explosion, operating error, mines, and collision. The Final Report followed on 6 August 1951. As reported through Thomas’s statement to the Commons, the Board concluded that material failure of the snort mast was the most likely immediate cause: the mast broke off without warning, the open induction admitted a rapid influx of water, the boat dipped by the stern, and sank. The Final Report has not been read directly for this article; every Board-language claim is reported as summarised in the Hansard statement and the secondary record.

Thomas’s statement set out the metallurgical tests on the recovered mast. The metallurgy of some parts was below standard, he told the House, and some of the welding was not good; it was also possible a major battery explosion had started a shock wave in the hull and ruptured the pressure trunking. He concluded that the evidence was insufficient to say with certainty why the boat was lost. The Director of Naval Construction, Sir Victor Shepheard, is reported, via Wikipedia, to have privately disagreed with the Board’s leading theory and preferred a battery-explosion reading. The underlying Admiralty papers have not been retrieved here; the disagreement is reported as reported, not as established.

The case has been raised twice since in the Commons, on 14 November 2007 and 24 January 2012. The 2007 debate elicited a statement, via TheyWorkForYou, that the Naval Historical Branch had reviewed the file and found no reason to disagree with the Board’s findings. The 2012 transcript is not in hand here. The seventy-five men are remembered at the Alderney memorial, unveiled on 16 April 2012, and at the Gosport memorial, unveiled in April 2013.

The evidence

The documentary record for Affray is unusually rich for a 1951 peacetime maritime loss. A Board of Inquiry visited the wreck via what was then the world’s first practical underwater television camera. A Cabinet minister admitted to Parliament that the Board could not fix the cause. A modern authorised dive survey has confirmed the externals. The central weakness is that nothing inside the pressure hull was ever recovered. Every theory below rests on external evidence and inference.

The wreck itself. Two independent inspections, fifty-six years apart, agree. The 1951 HMS Reclaim television survey recorded an intact hull listing slightly to port, all hatches shut, the search periscope and the ANF radar mast extended, the bow hydroplanes set to “rise hard,” and the snort mast broken off and lying on the seabed, attached by only a thin shred of metal. No other external damage was seen. In 2007, Dr Innes McCartney, author of Lost Patrols: Submarine Wrecks of the English Channel, returned to the site under Admiralty authorisation. His team reported the wreck “exactly as described by the Navy diving team in 1951.” The combined inspections rule out surface collision, mine strike, torpedo or external explosion. The pressure hull is not breached apart from the snort opening.

The recovered snort mast. The mast was the only component of Affray ever recovered. The Admiralty tested it. The metallurgy of parts was below standard, some of the welding was not good. Later analyses of the same test data drew a more difficult conclusion: the recovered mast should not have failed during normal operation. The defects were real but were not, on the test record, sufficient to explain a fracture under the routine snorting load on a 4.5-knot Channel transit. The mast was defective and it was not defective enough.

The extended periscope and radar mast. The position of both at the moment of catastrophe is the strongest single physical fact in the file. Extending the masts is the routine state of a snorting submarine. The wreck therefore shows the boat was snorting at the catastrophe. That configuration is consistent with snort-mast failure. It is also consistent with a battery event during snorting, because Affray’s configuration at the catastrophe is the configuration she would have been in for hours on a Channel transit. The two cannot be distinguished by configuration alone.

The closed hatches. No DSEA escape attempt was made. The hatches are sealed. The bow hydroplanes are set to “rise hard.” Both the 1951 team and McCartney’s read these as the signature of an instantaneous catastrophe. There was time to push the planes to full rise, a single lever action. There was no time to attempt escape.

The pre-sailing defect history. The snort had been faulty since fitment. A battery tank leak was scheduled for repair after the exercise. These are real and indirect; none of them, alone, connects to a fatal failure on 16 to 17 April. The battery tank leak is suggestive but does not prove a hydrogen event; an A-class battery vented hydrogen in normal operation, ventilated it through the snort, and was protected by interlocks against ignition.

Two configurations match the wreck: snort-mast failure, and a battery event during snorting. Both leave the periscope and radar mast extended, all hatches shut, the planes at “rise hard,” the boat intact except at the snort opening. The wreck cannot distinguish them. The recovered mast is defective enough to satisfy the prose of the official answer and not defective enough to satisfy the test data.

The theories

Everything in this section is a hypothesis. The Board stated a most likely cause; the First Lord then stated that the evidence was insufficient to be certain; the most senior naval architect of the day is reported to have disagreed with the Board’s leading theory in private. None of what follows has been established as the answer.

Snort mast metal-fatigue fracture. The Board’s reading. A latent defect in the mast failed under routine snorting load. The mast snapped, the open induction admitted a rapid influx of water, the boat dipped by the stern and sank. In its favour are the recovered broken mast, the documented defects, the snorting configuration, and the absence of other external damage. Against it stand the Admiralty’s own conclusion that the mast should not have failed in service, the Cabinet-level admission that the evidence was insufficient, and an early skeptical reading that the mast may have broken on impact with the seabed rather than caused the sinking. The official answer is itself hedged.

Battery explosion or hydrogen event in the pressure hull. The alternative Thomas named to the Commons: a major battery explosion that started a shock wave and ruptured the pressure trunking. On this reading the snort mast was broken off by the shock or by seabed impact, and is artefact rather than cause. In its favour are the uncompleted battery tank leak repair, the hydrogen-venting behaviour of an A-class battery, the instantaneousness of the catastrophe, and Shepheard’s reported private preference. Against it is the absence of any external evidence of hull rupture; none has been found. Nonetheless, this is the live alternative named at Cabinet level.

Failure of the snort induction valve, or operating error. Raised in the 14 November 2007 Commons debate. Failure to operate the snort head valve correctly, or material failure of the valve rather than the mast, could have admitted a rapid flooding event without the mast needing to fail in service. The broken mast is then explained by subsequent break-off or by impact with the seabed. In its favour are the boat’s snorting configuration, the documented snort-system defect history, and the thirteen-trainee complement that raises the prior probability of operating error. Against it stands the recovered mast itself, which is broken and needs an account either way. Not adopted by the Board.

A combination event. A synthesis, not a formal Board theory. The snort failed near the head valve, partial flooding reached the battery compartments, water on the lead-acid cells produced chlorine or arcing, the event was instantaneous. It explains every external observation without requiring either single mechanism to do all the work. The Board did not propose it.

Mine, collision, or hostile action. Historic Channel mine, collision with a passing ship, sabotage. All three would be expected to produce external hull damage. None is present. The Board considered and rejected. The reading is ruled out.

What remains unknown

At approximately 2115 hours on 16 April 1951, HMS Affray dived in the English Channel to begin a snorted transit at 4.5 knots. Some time between then and her missed 0800 surfacing the next morning, a catastrophe overcame her in seconds, while she was at periscope depth on snort. There was time to push the bow hydroplanes to “rise hard” and time for nothing else. The snort mast was broken off at or near the moment of catastrophe. The pressure hull was not breached. All seventy-five men aboard died.

The Board reported on 6 August 1951 that material failure of the snort mast was the most likely immediate cause. The Admiralty’s own tests then concluded that the mast should not have failed in service. The First Lord told the Commons that the evidence was insufficient to say with certainty why Affray was lost, and named a major battery explosion as a live alternative. The Director of Naval Construction is reported to have privately preferred that alternative. The Naval Historical Branch reaffirmed the Board in 2007. McCartney’s 2007 dive team found the wreck exactly as the 1951 team had described it. The Ministry of Defence’s position has not changed.

So we will not tell you the snort mast killed her, because the Admiralty’s own tests said it should not have failed in service. We will not tell you a battery explosion killed her, because no external rupture has been found and the Navy did not adopt the reading. We will not tell you the valve failed, because the mast is broken and a valve event does not predict that. The open question is the one Thomas posed in 1951. Was the broken mast on the seabed the cause of Affray’s sinking, or the artefact of a different and worse event inside the hull that has left no external trace? Seventy-five years on, that question is still on the file.

Sources

Primary / official

The Final Report of the Board of Inquiry, 6 August 1951, has not been read directly for this article. Every Board-language claim is reported as summarised in the First Lord’s 14 November 1951 Hansard statement.

Secondary / contextual

Wikipedia, HMS Affray (P421)
Submariners’ Association, HMS Affray Lost with all Hands
Royal Marines History, Loss of HM Submarine Affray and 4 Man SBS team
rnsubs.co.uk, Disaster Beneath the Waves
Diving Life, Forbidden Wreck: HMS Affray
The National Interest, The Royal Navy Lost an Attack Submarine and Still Can’t Explain Why
Innes McCartney, Lost Patrols: Submarine Wrecks of the English Channel (Periscope, 2003).