Flower-class Corvette

In 1939 the Royal Navy needed escort vessels in numbers it had no capacity to build. Its shipyards were committed to destroyers, cruisers and capital ships, and a destroyer took years and a skilled workforce that did not exist in surplus. What the Admiralty asked for instead was something that could be built quickly, in the small commercial yards scattered around Britain that had never constructed a warship in their lives.

The answer came from Smith’s Dock Company of Middlesbrough, a builder of fishing vessels, which offered a development of its whale catcher Southern Pride — a 700-tonne, 16-knot ship designed to chase whales in the Southern Ocean. A whale catcher was, after all, a small vessel built to hunt something large and fast in appalling weather. The Navy took the design, added a gun and depth charges, and called the result a corvette.

Everything about the Flower was subordinated to being makeable. She was around 62 m long and displaced about 940 tonnes — small enough for yards with modest slipways — and her machinery was a single triple-expansion steam engine, obsolete technology by naval standards and precisely the sort of plant that merchant-ship engineers already knew how to build, install and repair.

The result was a warship that could be laid down in a yard that had been building trawlers, and manned by crews largely made up of reservists and fishermen with a few months of training. They were named after flowers — Bluebell, Snowflake, Primrose, Snowdrop — which is where the class name comes from and which struck more than one officer as an odd label for a ship sent to hunt submarines in the North Atlantic. Between the Royal Navy and the Royal Canadian Navy, roughly 267 were built — published totals run to around 294 depending on whether the modified and Canadian-built variants are counted — and they arrived at a rate no purpose-built escort could have matched.

The price was paid by the men aboard. The Flower kept the whale catcher’s round-bottomed hull, which is excellent for riding out a sea and dreadful for staying steady in one, and her motion in the North Atlantic became legendary: her crews said she would roll on wet grass. In heavy weather she rolled through arcs that made cooking, sleeping and accurate work with instruments equally impossible.

The early ships also had a short forecastle, so the seas came aboard and stayed there. Life on an Atlantic escort meant being permanently wet, permanently cold and chronically exhausted, in a hull the size of a large trawler, for voyages of two weeks at a time. The corvettes were not merely uncomfortable in the way warships are uncomfortable: they were notorious throughout the Navy.

Her fundamental limitation was speed. The Flower made 16 knots at best, and a Type VII U-boat on the surface made about 17.7. A corvette could not run one down. If a U-boat was sighted on the surface and chose to withdraw, it simply left — the escort was left in its wake, unable to close the range and unable to leave the convoy it was protecting to try.

What the corvette could do was force the boat under, and that was the whole of her tactical value. A submerged Type VII made a few knots and quickly exhausted its batteries, and a submerged U-boat could not attack a convoy that was steaming away from it. The margins were small and they were the ones that mattered: a convoy made perhaps 7 to 9 knots, so the escort had speed enough to patrol around the columns and rejoin them, and never enough to chase. The Flower’s job was less to sink submarines than to keep them down, keep them away and stay between them and the merchant ships — work measured in cargoes delivered rather than in kills claimed.

Her armament was modest and largely elderly: a single 4-inch (102 mm) gun of First World War vintage on the forecastle, light anti-aircraft weapons, and the real armament — depth charges, around 40 of them, rolled off the stern and fired out to the sides by throwers. Detection was by ASDIC, which found a submerged boat but lost contact in the final moments of an attack run, precisely when it was needed.

That gap was closed by Hedgehog, an ahead-throwing mortar that fired a pattern of contact-fused bombs in front of the ship while the ASDIC still held the target. Combined with better radar, high-frequency direction finding and — decisively — escort groups trained to work together rather than as individual ships, it turned the corvette from a deterrent into a killer during 1943.

No navy was transformed by the Flower more than Canada’s. The Royal Canadian Navy entered the war with a handful of destroyers and finished it as one of the largest escort forces in the world, and it did so overwhelmingly on corvettes built in Canadian yards — often crewed by men who had never seen the sea before enlisting.

They took a disproportionate share of the worst duty: the mid-Atlantic gap, the stretch beyond the range of shore-based aircraft where the U-boat packs concentrated, and the long grinding convoy battles of 1942–43 in which whole escort groups fought for days without relief. The Canadian corvette became the emblem of a navy improvised from nothing in three years.

The corvettes were designed for the Atlantic and spent a good part of the war somewhere else. From 1941 Flowers escorted the convoys supplying the Eighth Army in Egypt and those that fought their way through to Malta from Gibraltar and Alexandria; HMS Delphinium worked the theatre continuously from 1941 to 1943, finishing with the invasion of Sicily. In November 1942 a large number of them shepherded the troopships of Operation Torch to the North African beaches, and some closed the shore to add their 4-inch guns to the bombardment.

The Mediterranean exposed what the design had not been drawn for. In the Atlantic the enemy was the submarine and the corvette’s weakness was speed; in the narrows the enemy was the aircraft, and the weakness was anti-aircraft armament — one 4-inch gun and a handful of light weapons, in a sea with no mid-ocean gap and no stretch out of reach of a shore-based bomber. The ships assigned to the Malta run were rearmed with heavier close-range weapons as fast as the yards could take them.

The Flower was not a good warship, and she was never asked to be one. She was slow, cramped, lightly armed and so uncomfortable that her own crews joked about her; a purpose-built escort — the River-class frigates that eventually replaced her — was better at the job in every measurable way. What the Flower had was that she existed, in 1940, in numbers, at a moment when the alternative was convoys with no escort at all.

She is also the ship in which the Battle of the Atlantic is remembered, largely thanks to Nicholas Monsarrat, who served in corvettes and turned the experience into The Cruel Sea. That is a fair outcome. The campaign was not won by the famous ships hunting the famous raiders, but by hundreds of small, ugly, converted whale-catchers keeping station on merchant convoys in weather that would have kept anything else in harbour.

• Roger Chesneau (ed.), Conway’s All the World’s Fighting Ships 1922–1946 (Conway Maritime Press).
• Angus Konstam, Flower Class Corvette 1939–45 (Osprey, New Vanguard).
• Nicholas Monsarrat, The Cruel Sea (Cassell) — a novel, written by an officer who served in corvettes.