The British Trick That Made German Soldiers Shoot Their Own Submarines

It is the autumn of 1942 and somewhere in the gray heaving waters of the Bay of Bisque, a German yubot is running on the surface.

She has been at sea for three weeks and her crew of 44 men are tired, hungry, and ready to go home.

The base at Laurel is perhaps 6 hours away.

The commander is standing in the conning tower, scanning the horizon.

Nothing, just cloud and white caps and the smell of diesel exhaust.

He gives the order to maintain course.

Then the lookout hears it, a low rhythmic thrming.

It comes from the south.

The commander raises his binoculars and squints into the morning light, but there is nothing to see.

The sound grows louder, closer.

And then at last, he spots the silhouette.

A twin engine aircraft low and fast skimming the wavetops.

British RAF Coastal Command.

His stomach drops.

He screams the order to dive.

The alarm bell hammers through the boat.

Men tumble down ladders and hatches slam shut.

The diesel engines cut and the electric motors take over and the submarine begins to slide beneath the surface.

On the surface, the aircraft roars past.

No bombs fall.

No depth charges.

The crew catch their breath.

They made it.

What they do not know, what none of them can possibly know, is that the aircraft already did its job.

Not by dropping anything, not by firing anything, but by switching off a light.

The technology involved was so simple that it barely qualifies as a piece of equipment at all.

It was a light bulb in a housing.

But the idea behind it, the tactical principle that made it extraordinarily lethal, was one of the most elegant deceptions of the entire Second World War.

It exploited not a weakness in German engineering, but a weakness in German biology, in the way human eyes work, in the way a man standing in a conning tower, squinting against the glare of the sky, simply cannot see something that is by any reasonable measure right in front of him.

This is the story of the Lee light and the men who used it to turn the Bay of Bisque into a killing ground.

It is a story about the science of seeing and not seeing.

about the gap between when a predator spots its prey and when the prey can spot the predator back.

And about how a retired RAF wing commander named Humphrey Diver Lee solved one of the most vexing tactical problems of the naval war with a piece of equipment that any reasonable person would have dismissed as absurdly straightforward.

To understand why the Lee light mattered, you have to understand what the Yubot war looked like in its early years and how close Germany came to winning it.

Between 1940 and 1942, the Atlantic was a catastrophe for the Allies.

German submarines were sinking merchant ships faster than they could be built.

In 1942 alone, more than 1,600 Allied vessels were lost to enemy action, the majority to Yubot.

The raw numbers are staggering.

Even now over 6 million tons of shipping destroyed in a single year.

The convoys carrying food, oil, ammunition and war material from North America to Britains were hemuriching cargos and crews at a rate that Churchill privately believed could lose the war outright.

He later wrote that the only thing that truly frightened him during the whole conflict was the Yubot peril.

The Germans had developed a tactical innovation of their own that made them extraordinarily difficult to counter.

Hubot, it turned out, were far more effective when they attacked on the surface at night rather than submerging and using torpedoes from depth.

On the surface, a submarine could travel at nearly 18 knots, fast enough to outrun many escort ships and to reposition for multiple attack runs.

Submerged, the same boat was reduced to perhaps seven knots, and her battery power lasted only so long.

The ocean at night was enormous in black, and a lowprofile submarine barely 2 m above the water line was almost impossible to spot visually.

Radar ought to have solved this, and to some extent, it did.

Early air-to-surface vessel radar sets known as ASVI could detect a surfaced yubot at ranges of several miles, which was revolutionary.

Coastal Command aircraft fitted with AS5 could vector in on a contact in the dark, prosecuting attacks that would have been utterly impossible a year before.

In the first months of AS5 use, results were encouraging.

But then the Germans adapted.

In the summer of 1942, the Marine began fitting Yubot with a device called the Mtox receiver.

A simple radar detection set that could pick up the emissions of British ASV radar at a range significantly greater than the radar itself could detect the submarine.

In effect, the Yubot heard the aircraft coming before the aircraft could see the hubot.

The moment a met lit up its warning lamp, the crew dived.

By the time the aircraft arrived at the last known position, there was nothing on the surface but a spreading patch of disturbed water and perhaps a few bubbles.

The Mtox transformed the tactical situation almost overnight.

Sinkings attributed to aircraft plummeted.

Coastal command squadrons were flying hundreds of hours of patrol time and achieving almost nothing.

The Bay of Bisque, the crucial transit route that every hubot had to cross to reach the Atlantic and return, became a sanctuary rather than a hunting ground.

The mathematics were depressing.

An aircraft could spend 8 hours on patrol and never once make a successful attack.

Crews became demoralized.

Commanders wrote increasingly frustrated reports.

The window of vulnerability, the brief period during which a diving submarine was still near the surface, was exactly what needed to be exploited.

But the darkness that the Ubot used as cover during their surface transits made them invisible even when radar had located them.

A radar contact gave a bearing and a range.

It could not tell you the exact angle of approach for a bomb run.

It could not illuminate a target for a visual attack.

And at the altitudes and speeds involved, attacking a target you could not actually see was effectively impossible.

What was needed was a way to illuminate a submarine during that final critical approach without giving it enough warning to dive.

Something that would be invisible until it was too late.

The man who solved this problem was not an engineer by training.

Humphrey Dverd Lee was a wing commander who had served in the Royal Flying Corps during the First World War and had spent the inner war years in the RAF before retiring.

He was not a scientist.

He was not attached to any of the prestigious research establishments that produced so many of the war’s technical innovations.

He was in the most literal sense an amateur in a world of professionals.

Lee’s insight was deceptively simple.

The problem was darkness.

The solution was light.

But not just any light.

A very specific kind of light controlled in a very specific way.

His device was at its core a powerful search light mounted in the nose or beneath the wing of a maritime patrol aircraft.

The light itself was initially a 24-in carbon arc lamp drawing around 90 amps, producing approximately 60 million candela of focused intense white light, enough to illuminate a surface submarine at ranges of up to one nautical mile.

The housing rotated on a hydraulic mount, allowing the crew to train it independent of the aircraft’s heading, which was crucial for the final moments of a diving attack run.

But the critical innovation was not the light itself.

It was the switch.

The aircraft would pick up a radar contact in the dark and begin its approach using the ASV set.

The radar gave them the range and bearing.

It would fly in at low level, often as low as 50 m above the water, closing the distance in the dark.

The Yubot’s METOX receiver was scanning for radar emissions, and if the aircraft had been using its radar continuously, the warning would have been received, and the submarine would have dived long before the aircraft arrived.

So the crew switched the radar off.

Some miles out, typically around 5 to 8 km, the navigator would shut down the ASV transmitter.

No radar emissions meant no Mtox warning.

The aircraft continued its approach on dead reckoning, guided by the last known position and the crew’s own judgment.

The submarine on the surface had no idea anything was coming.

Then at roughly 1 mile out, close enough that even a crash dive would leave the submarine stern and propellers exposed.

Close enough that the depth charge run could be completed before she could reach safety.

The crew switched the Lee light on.

The effect was instantaneous and devastating.

After flying for perhaps 10 minutes in total darkness, the crew of the hubot suddenly found themselves bathed in blinding white light.

The transition from darkness to that intensity of illumination left their night adapted eyes completely unable to function.

They were in the most immediate sense blind.

They could hear the aircraft.

They could do nothing useful about it.

They could not man the anti-aircraft guns effectively.

They could not judge distances.

They could not see the depth charges falling.

The attacking aircraft, meanwhile, had all the information it needed.

The light revealed the submarine clearly.

The crew could make final adjustments to their attack line.

The depth charges, typically a stick of six set to detonate at shallow depth, went into the water across the submarine’s path, and the results were frequently lethal.

Lee worked on early prototypes through 1941, often using his own savings and requisitioned equipment.

The development program was conducted partly at the aircraft and armament experimental establishment at Bosam down and partly through trial and error.

The first operational Lee light was fitted to a Wellington bomber of number 172 squadron coastal command and the unit began operations in June 1942.

The first confirmed kill using the Leite came on the 4th of July 1942 when a Wellington of number 172 squadron attacked the Italian submarine Luigi Toulli in the Bay of Bisque.

The Luigi Terelli was severely damaged and forced to return to port.

The psychological impact of the attack, the sudden inexplicable appearance of blinding light from a dark sky, was noted in the surviving cruise accounts as profoundly disorientating.

Over the following months, the Lee Light began to reshape the tactical balance in the Bay of Bisque in ways that went beyond the simple arithmetic of submarine sunk.

Yubot commanders who had previously crossed the bay on the surface night after night with confidence that their Mettox receivers would give them adequate warning now found themselves uncertain.

The darkness that had been their ally was no longer reliable.

Light could appear from nowhere.

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The German response was initially confusion.

After several attacks that seem to have come from aircraft not using radar, the marine began investigating whether the British had developed some entirely new detection system, infrared perhaps, or acoustic.

Carl Donuts, the commander of the Yubot arm, received increasingly baffled reports from returning captains.

The aircraft had appeared without warning.

There had been no radar signal on the Mtox.

How is it possible? The answer that the British had simply turned their radar off and used a torch was so straightforward that it took some time to arrive at.

When it did, the Germans implemented their own counter measures, mounting heavier anti-aircraft armament on hubot and attempting to fight back on the surface rather than diving.

This produced a brief and costly period in which submarines engaged aircraft in open gun battles with mixed results for both sides.

The closest German equivalent to the Lee Light was the Shineer system developed for their own maritime aircraft, but it was never employed with the same tactical sophistication, and German longrange maritime patrol capability was considerably more limited than that of coastal command.

The Americans, for their part, adopted a modified version of the Lee Light for their own patrol aircraft in the Atlantic and Pacific theaters, acknowledging the British systems effectiveness and largely duplicating its technical specifications.

The crucial difference between the Lee Light and other Allied illumination methods lay in the integration between radar, navigation, and the light itself as a weapon system.

American approaches tended toward more powerful but less precisely employed illumination.

The British method, the extended radar blackout followed by sudden full illumination at close range, was a tactical doctrine as much as a piece of technology.

And it was the doctrine that made it lethal.

German engineers did in relatively short order develop radar detection equipment capable of picking up the shorter wavelength radar sets that eventually replace the original AS5 in British aircraft.

The introduction of the centimetric ASV Mark III operating on a wavelength that existing MTO sets could not detect extended the effectiveness of the radar and lee light combination considerably.

By the time the Germans had developed appropriate countermeasures, the broader battle of the Atlantic had shifted decisively in the allies favor.

The comparison that matters most, however, is not technical, but numerical.

In the first half of 1942, before the Lee Light entered service, coastal command aircraft flying over the Bay of Bisque were achieving roughly one attack per 350 flying hours.

In the 6 months following the Lee Lights introduction, that figure improved dramatically with estimates suggesting an attack rate several times higher.

Exact figures remain partially classified, but the direction of the trend is not in dispute.

The legacy of the Lee Light is in the end a story about the multiplying effect of a single tactical insight.

The device itself was not particularly advanced.

The light source was comparable to those used in film projectors of the period.

The hydraulic mount was solid engineering but hardly extraordinary.

The total weight of the installation, roughly 270 kg in early versions, was significant but manageable.

What made it decisive was the recognition that the enemy’s countermeasures could be defeated not by superior technology but by superior tactics.

The MTOX receiver was a genuinely effective piece of equipment.

It did exactly what it was designed to do, but it could only detect what was being transmitted.

And if you stop transmitting, it had nothing to detect.

The weakness was not in the German equipment.

It was in the German assumption that the British would always be using their radar.

Donuts’ logs from late 1942 and early 1943 reflect a growing unease about the Bay of Bisque that goes beyond the tactical into something approaching existential uncertainty.

He could not explain the losses.

He could not reliably reconstruct what was happening to submarines that failed to return.

The absence of information was as damaging as the losses themselves because it meant he could not develop effective countermeasures.

He was fighting a threat he could not fully characterize.

The Leight is not a famous weapon.

It does not appear in the popular iconography of the Second World War.

It is not the Spitfire or the Lancaster.

But the argument can be made, and the numbers broadly support it, that the Battle of the Atlantic, which Churchill considered the war’s most critical campaign, was materially influenced by a piece of equipment that a retired wing commander designed partly on his own initiative, using his own funds, working around the edges of an establishment that was initially skeptical of his idea.

Examples of the Lee Light survive in several British aviation collections, including examples associated with surviving Vicer’s Wellington aircraft.

The device itself is modest in person, a cylinder of metal and glass mounted on a bracket.

It does not look like something that changed the course of a war, but that is rather the point.

Return for a moment to that yubot in the Bay of Bisque in the autumn of 1942.

The aircraft passed.

No bombs fell.

The crew surfaced again an hour later, continued on their heading, and eventually reached Lauron.

They were the lucky ones.

The crew that happened to be in the wrong place at the wrong time for the British aircraft, but early enough that the Lee light was not yet fitted to every patrol.

By the following spring, the situation would be very different.

Hubot crossing the Bay of Bisque were dying at a rate that shook the marine to its foundations.

The months of May 1943 alone saw 43 yubot sunk.

A loss rate so catastrophic that Donuts temporarily withdrew his forces from the North Atlantic entirely.

The combination of improved radar, better convoy escort tactics, long range patrol aircraft, and the Lee Light had turned the transit route into a gauntlet that an increasing proportion of submarines simply did not survive.

The crews knew it.

Letters home from Yubot men in this period carry a fatalistic quality that was not present even a year before.

They speak of the bay as a place to be feared, of aircraft appearing from nowhere, of the light that came without warning, of friends who set out and never came back with no explanation, no wreckage, no survivors to report what had happened.

Death in the Atlantic was often like that.

complete, silent, leaving nothing behind.

Humphrey Lee received the Legion of Merit from the United States and was officially credited with the invention of the device that bore his name.

He died in 1964, a relatively obscure figure, even by the standards of wartime inventors.

His innovation does not feature prominently in the standard histories.

It is not the subject of feature films.

But consider what it achieved.

a device that cost almost nothing compared to a bomber, a warship, or a convoy that required no exotic materials and no advanced science that could be understood in principle in about 30 seconds.

And that helped ensure that the ocean bridge between North America and Britain, the lifeline on which the entire Allied war effort ultimately depended, was not cut.

The Germans tried jamming.

They tried better radar warning systems.

They tried fighting back with heavier guns.

They tried changing their transit routes and their timing and their depth protocols.

None of it was enough because the weapon being used against them was not in the end a light at all.

It was the understanding that the most effective deception is one that uses the enemy’s defenses against themselves.

Turn off the radar.

Wait for the darkness to do its work.

Then when it is already too late to matter, switch on the