HMS Snowflake (K211): The Corvette at the Turning Point of the Atlantic

Built by Smith's Dock

HMS Snowflake was built by Smith's Dock Company, ordered on 3 August 1940, with construction beginning the following May, launched on 22 August 1941 and commissioned on 2 November that year, a Flower-class corvette destined for the unglamorous, exhausting work of convoy escort that defined the Battle of the Atlantic. Command went to Lieutenant Harold Chesterman, an Australian-born RNR officer in his mid-twenties, who would go on to lead her through the single most consequential fortnight any Flower-class corvette ever had.

Chesterman is worth more than a line. He was born in Queensland and sent to sea young in the most literal sense: at fourteen his father put him aboard a ship in Brisbane, alone, bound for London and the Thames Nautical Training College in the old wooden two-decker Worcester, which is where British merchant officers were made. He was in the merchant service when the war began, was called up as a Royal Naval Reserve officer, and was torpedoed twice before he ever got a command of his own. When he did, at twenty-five, he was reckoned to be the youngest officer commanding a major warship in the Royal Navy. He finished the war with the MBE, the Distinguished Service Cross and Bar and the Reserve Decoration, and none of it came from a peacetime career path.

Six Torpedoes and Ten Attacks

By the time she met her defining test, Snowflake was already a convoy veteran, having escorted the Arctic convoys PQ 15 and QP 11 in the spring of 1942, the same operation during which the cruiser HMS Edinburgh was fatally torpedoed while carrying a fortune in Soviet gold. Snowflake's own defining moment, though, came during Convoy ONS 5 in April and May 1943, one of the largest and most consequential convoy battles of the entire war. She remained continuously in action, engaging U-boat contact after U-boat contact and recording ten separate anti-submarine attacks during the running battle.

At one point the submarine U-532 fired six torpedoes at her, the closest passing a mere twenty yards away, a narrow escape that gives some sense of just how close and desperate this fighting had become.

What ONS 5 Actually Was

The numbers matter here, because "one of the largest convoy battles" does not convey it. ONS 5 left Liverpool on 21 April 1943 with forty-two merchant ships, westbound and mostly in ballast, escorted by Commander Peter Gretton's Escort Group B7: the destroyers Duncan and Vidette, the frigate HMS Tay (K232), and the corvettes Snowflake, Sunflower, Pink, Loosestrife and HMS Alisma (K185). Waiting for them, in two wolfpacks called Star and Fink, were forty-three U-boats. That is roughly one submarine for every merchant ship, and it was the largest concentration Karl Dönitz ever managed to put against a single convoy.

The battle ran for seven days across the first week of May, in weather that was itself an enemy. A full gale scattered the convoy, so that at one point Gretton had ships spread over a hundred miles of ocean, and the corvette Pink ended up shepherding her own private convoy of stragglers and sinking a U-boat while doing it. The escorts were exhausted, several were damaged and all of them were short of fuel and depth charges. When it finished, thirteen merchant ships had been sunk, some sixty-three thousand tons. Six U-boats had been destroyed outright and seven more so badly damaged that they had to go home.

There is one detail usually left out, and it changes the shape of the story. Gretton was not there at the end. Duncan ran low on fuel and the sea was too heavy for him to take any from the tanker sailing with the convoy for exactly that purpose, so on 4 May he had to break off for Newfoundland, and command passed to Lieutenant Commander Robert Sherwood in Tay. Sherwood was a Royal Naval Reserve officer, a merchant navy man like Chesterman, and it was under him, on the last three nights, that a scratch force of tired escorts destroyed most of the U-boats. The most important convoy battle of the war was won by the reservists after the regular officer commanding had been forced to leave.

A Confirmed Kill, and a Grim Aftermath

On the night of 5-6 May 1943, in thick fog, the destroyer HMS Oribi rammed the German submarine U-125 at nearly twenty knots, leaving her crippled and unable to dive. Snowflake found her by radar less than an hour later, closed to within a hundred metres and lit her up with searchlights; rather than be captured, U-125's own crew scuttled their boat with explosive charges set almost alongside Snowflake herself.

What followed was one of the battle's grimmer footnotes. With dozens of German sailors now in the freezing sea, the escort's senior officer, aboard HMS Tay, radioed back that picking up survivors was "not approved," and Snowflake and HMS Sunflower turned away to rejoin the convoy, leaving all 54 of U-125's crew to die in the water that night.

For years, Allied records credited Snowflake and HMS Duncan with a second kill a fortnight later, the sinking of U-381 on 19 May, but a postwar review of German transmission logs told a different story: that depth-charge attack actually fell on U-304 and U-636, both of which escaped undamaged, while U-381 herself had already vanished without trace over a week earlier, her loss never satisfactorily explained and all 47 of her own crew lost with her. The real tally still made Snowflake one of the more effective escorts of the entire ONS 5 battle, which remains widely regarded by historians as a genuine turning point in the Battle of the Atlantic.

Turning point is a phrase that gets used loosely, so it is worth saying what happened next. ONS 5 was the opening of what the Germans came to call Black May. Across that month the U-boat arm lost forty-one boats, roughly a quarter of the operational force, for a rate of exchange that no navy could sustain. On 24 May 1943 Dönitz ordered the wolfpacks out of the North Atlantic altogether. They came back later in the year with new weapons and new tactics, and they never regained the initiative. Six U-boats sunk in one week by seven small ships is the arithmetic of that, and HMS Pelican (F86), who came out with the support group that reinforced ONS 5 at the critical moment, tells the same week from the other end.

From Warship to Weather Ship

With the war won, Snowflake was converted at Rosyth in 1947 for a very different purpose, renamed Weather Watcher and sent to keep station at Ocean Weather Station Alpha, using her small, seaworthy hull to gather meteorological data in the same Atlantic waters where she had once hunted submarines, a fittingly watchful second career for a ship whose wartime reputation rested on spotting things first. Chesterman himself was recommended for the Distinguished Service Cross by his friend and ONS 5's own escort commander, Peter Gretton, and went on to add a Bar to that same decoration before the year was out.

The weather ship years were not a retirement, whatever the gentle name suggests. When the war ended, the world had discovered that it wanted to fly the Atlantic, and flying the Atlantic in a piston-engined airliner with no satellites and no mid-ocean forecasting was a genuinely dangerous business. So the new International Civil Aviation Organization agreed in 1946 a network of ocean weather stations, fixed points in the middle of the sea where a ship would sit for weeks at a time taking readings, sending up radiosonde balloons, providing a radio beacon for aircraft overhead and standing by to pick up anybody who came down in the water. Britain took several of the stations, and the ships it used were mostly Flower-class corvettes, because they were cheap, immensely seaworthy and suddenly surplus.

So Snowflake spent fourteen years, longer than her entire war, riding out North Atlantic weather at a fixed position for the benefit of people who would never know she was there. The observations those ships made are still in the climate record and are still being used, which is a peculiar kind of afterlife for a corvette. She was not the only one of her class to end up doing it: HMS Bryony (K192), who was bombed to the bottom of her own fitting-out berth before she was finished, went the same way afterwards.

After her final voyage out to Station Alpha in December 1961, she was eventually broken up in Dublin in May 1962, closing out a career that had taken her from the sharpest edge of the Atlantic convoy war to the quieter, equally essential work of watching the weather.