In the years leading up to the First World War, Britain’s Royal Navy faced an existential challenge. Germany’s naval expansion, and especially its submarine warfare, forced the Admiralty to rethink what the future of sea power would look like. The dreadnought battleship still ruled the waves, but underwater warfare was evolving with a speed that made planners uneasy. In this atmosphere of urgency, innovation, and fear, the British instructed its engineers to build a submarine that was fast enough to operate with the battle fleet.
The result was the K-class submarine, a vessel so ambitious and so compromised that it earned a darkly comic set of nicknames— “Kalamity class” and “Killer class”. The K-class proved to be the deadliest warship ever built, but only for those who sailed them.
British submarine K15. Credit: Wikimedia Commons
Most submarines of the era were slow, lurking predators meant for independent attack missions. But British admirals wanted something different. They imagined submarines working with the main fleet—running on the surface at the high speeds required for reconnaissance and screening operations, then diving to attack when needed.
To achieve this, the K-class received what no other submarine ever had. It had massive steam turbines, capable of pushing the boats to more than 21 knots on the surface, and fast enough to keep up with battlecruisers.
But speed came with extraordinary complexity. The K-boats needed oil-fired boilers, funnels for exhaust, large air intakes and giant hulls over 330 feet long, as big as light cruisers. When a K-class submarine needed to dive, the crew had to shut down the boilers, retract the funnels, seal the intakes, and convert to electric motors—a process that took far too long for emergency combat. This meant that when a submarine was attacked on the surface, a crash dive was impossible. While a well-drilled U-boat could dive in 90 seconds, the K-boat crew would be doing well to get below in less than five minutes.
There was also the problem off maneuverability. Their long hulls resisted turning and tended to “plough” underwater, leading to sudden uncontrolled dives.
The story of the early K-boats was a catalogue of disasters.
Submarine K4 stranded on Walney Island. Credit: Wikimedia Commons
K13 sank to the bottom of Gareloch during sea trials when an intake failed to close whilst diving and her engine room flooded. 32 seamen lost their lives. K2 caught fire on her first dive. K3 plunged to the bottom of the Stokes Bay on a test dive. K1 collided with K4 off the Danish coast and was scuttled to avoid capture. K5 was lost during a mock battle. K15 sank at her mooring in Portsmouth.
Despite these setbacks and the mounting loss of lives, the Admiralty pressed ahead for three years with K-boats, even though the plan of their eventual use—in close formation with the battle fleet—was fraught with danger as evidenced by the incident of January 31, 1918.
The Battle of May Island
That evening, around forty naval vessels left Rosyth on the Firth of Forth, Scotland, bound for Scapa Flow in Orkney where exercises involving the entire Grand Fleet would take place the following day. Among them was the 5th Battle Squadron of three battleships with their destroyer escorts, the 2nd Battlecruiser Squadron of four battlecruisers and their destroyers, two cruisers and two flotillas of K-class submarines.
The fleet moved in long, blacked-out columns, carefully spaced with only a dim blue stern light that was shielded to block visibility from the sides. All ships maintained strict radio silence to avoid attracting possible lurking enemy ships.
The night was clear and the seas relatively calm, but the moon had not yet come up. At approximately 19:00 hours, the lead vessel battlecruiser HMS Courageous passed the Isle of May just as a low-lying bank of mist settled over the sea.
As the flotilla passed the island, a pair of minesweepers sprang out of nowhere forcing the vessels to alter course sharply to port to avoid them. At that moment, the helm of K14 jammed and she veered out of line. Seeing the K14 unable to alter her course, the boat behind her, K12 turned on her navigation lights and so did K14. However, the submarine K22, which was following the K12, lost sight of the rest of the flotilla in the mist, veered off the line and struck K14, killing two men.
Aware of the stricken ships ahead, HMS Fearless came to a stop and signaled that she did so. K4 also came to a stop, but the trailing boats did not. K3 narrowly missed K4 and then stopped three cables further on, but K6, despite going full astern, could not avoid a collision, ramming the broadside of K4 and nearly cutting the latter in half. The seriously damaged K4 sank with all of her crew; while going down, she was hit by K7.
The bow of the cruiser HMS Fearless after colliding with the submarine K17. Credit: Wikimedia Commons
Meanwhile, the K22 sent up distress signals, and the HMS Ithuriel responded by turning around and leading the 13th Submarine Flotilla towards the sinking boats. As the 13th Flotilla reached the Isle of May, they encountered the outbound 12th Submarine Flotilla. Fearless, the leader of the 12th Flotilla, was moving at full speed, and rammed the K17, damaging Fearless' bow, and sinking the K17.
At this point the 5th Battle Squadron of three battleships and their destroyers passed through the area, unaware of what had happened, with some of the destroyers cutting down the survivors of K17 struggling in the water. Only nine of the 56 men originally on board the submarine survived, and one of these died of his injuries shortly afterwards. A total of 48 men from K17's crew were lost.
Within 75 minutes, two submarines had sunk, three had been badly damaged, and 105 men had been killed. Because the incident happened during wartime, and because the Admiralty feared public embarrassment and morale damage, details were tightly suppressed and not released until 1994.
The name “Battle of May Island”—a bit of sailor’s gallows humour—stuck. It was not a battle, and no enemy was present, yet it resembled a chaotic naval engagement fought entirely by British ships against each other.
The disaster did not immediately end the K-class program, but it destroyed confidence in high-speed steam submarines. After the war, the Admiralty quietly retired the boats, acknowledging that the concept was flawed. Submarine doctrine shifted back to diesel-electric propulsion and independent attacks—roles submarines were actually suited for.
References:
# The ‘Battle’ of May Island. Naval Historical Society of Australia
# Reflecting on a dark for the navy. The Scotts Magazine
# Battle of May Island. Wikipedia
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