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If Adolf Hitler’s threat to invade Great Britain in the summer of 1940 was a bluff, it was a bluff carried through with exhaustive German thoroughness. Even as the German navy began to gather thousands of commandeered river barges and motorboats in ports flanking the Channel, Nazi planners were working out every last detail for their impending occupation of defeated Britain.

The newly created Military Economic Staff England drew up lists of goods and factories to be seized hard on the heels of advancing German forces as they swept north from their landing beaches in southern England: agricultural products, fuels and oils of all kinds, metal ores and products of all kinds, gems and precious metals, rubber, leather, hides, timber. Quartermaster officers carefully calculated the proper exchange rate between British and German currency, circulating a memorandum establishing precisely 9.60 Reichsmarks as the equivalent of one pound sterling, 48 Reichspfennigs as one shilling.

In France, prison camps were methodically erected: under an order signed by the army commander-in-chief, Field Marshal Walther von Brauchitsch, Britain’s entire population of able-bodied males between the ages of 17 and 45 was to be “interned and dispatched to the Continent with a minimum of delay,” to swell the slave labor force of the burgeoning Reich.

Professor Franz Six, an SS colonel who would later oversee the executions of more than a hundred local political commissars in the Nazi invasion of Russia, was placed in charge of six SS Einsatzgruppen detailed to carry out the immediate arrests of 2,300 leading politicians, intellectuals, civic leaders, émigrés, and Jews in Britain whose names were on a list the Gestapo had prepared. The list included Winston Churchill and his cabinet; the editors, publishers, and top reporters of all major British newspapers; the exiled Czech president Eduard Benes; the philosopher Bertrand Russell; the writer E. M. Forster; the playwright and composer Noel Coward; and the Boy Scouts’ leader and founder Robert Baden-Powell.

The Germans had even prepared notices in English advising the populace that any “thoughtless actions,” “any passive or active opposition,” “any insult” to Germany, “any disobedience” to orders would “incur the most severe retaliatory measures.”

A “Proclamation to the People of England,” personally signed by Brauchitsch, added a more specific threat. “I warn all civilians that if they undertake active operations against the German forces, they will be condemned to death inexorably.”

If it was a bluff, it was a bluff Great Britain had no choice but to take with deadly seriousness. In late June 1940, imagining the worst, Churchill ordered preparations for Britain’s last stand: in complete secrecy, an underground army would be organized, trained, and equipped, with the mission of waging desperate guerrilla warfare behind the enemy’s lines if the invasion came. The man who would lead the effort, Maj. Colin McVean Gubbins, told his officers to scour the country for men “who knew the forests, the woods, the mines, the old closed shafts, the hills, the moors, the glens—people who know their local stuff.” Within weeks, the first cells of Britain’s resistance-movement-to-be were digging hideouts, preparing explosive booby traps, and steeling themselves for a battle in which neither side would show the least mercy.

Although Britain was never quite as defenseless in the grim months following the fall of France as later legend would have it (fanciful stories would abound for years of local units ransacking museums for Napoleonic-era howitzers, or even pikes, to arm themselves), the military calculus was stark. The British naval staff warned that even the full might of the Royal Navy, still the most powerful in the world, could not prevent the Germans from bringing ashore 100,000 troops in an initial landing. Although 190,000 of the 250,000 British troops sent to France had made it back safely following the evacuation at Dunkirk in June 1940 (as well as some 140,000 French troops), almost none of their tanks, artillery, or antitank weapons had made it back with them.

Hitler’s forces, for now unchallenged anywhere on the Continent, could pick the time and place to strike; initial plans for the invasion—now code named Operation Sealion—called for 34 divisions to land in two major waves, bringing with them 40,000 trucks, 60,000 horses, and 650 tanks. Gen. Erwin Rommel was to lead one of the panzer columns that would encircle London in a blitzkrieg pincer movement. Two airborne divisions would seize and bridge the Royal Military Canal—a barrier created during the Napoleonic Wars to stop the French, and a significant antitank obstacle between the south coast and London.

In all of Britain there was a total of 27 regular army divisions to meet the invaders; only a half-dozen of those were equipped with much more than rifles. There were only 350 tanks in the whole country, far too few to cover hundreds of miles of coastline with the mobile reserve that was the linchpin of a successful counterattack. There were fewer than 200 antitank guns in Britain, and Churchill himself instructed that given the extreme shortage of antitank rounds—one crew he inspected had only six per gun—not a single one could be spared for practice, even to acquaint the crews with how their weapons worked. “Fire should be held for the last moment at the closest range,” the prime minister ordered.

Throughout the summer, as the Battle of Britain raged in the skies overhead, a shadow war of threat and defense, bluff and counterbluff, unfolded on sea and land. Hitler hoped to convince Britain that resistance was futile, now that it stood alone against the undistracted might of Nazi Germany; Churchill sought to establish that resistance, on the bloodiest imaginable scale, was inevitable.

Across Britain, 18,000 concrete pillboxes sprang up along the coasts. Barbed wire and minefields covered beaches, mazes of antitank obstacles appeared on roads. Railway station signs were taken down or painted over. Bridges were wired with explosive charges, readied for demolition.

From the United States, a half-million rifles and 900 75mm field pieces arrived by ship to equip the Home Guard, a hastily organized militia of volunteers too old or infirm to join in the regular army. It would be the source of jokes throughout the war—Noel Coward wrote a humorous ditty portraying an elderly Home Guard colonel writing a beseeching letter to the minister of supply: “Would you please oblige us with a Bren gun?” But 1.5 million men promptly volunteered, underscoring the dead earnest in which the country took the invasion threat.

“The land defences and the Home Army are maintained primarily for the purpose of making the enemy come in such large numbers as to afford a proper target to the sea and air forces,” Churchill explained in a memorandum on August 5, 1940, “and to make hostile movements and preparations noticeable.” Within weeks, all indications—the confluence of German preparations, the tides, and the moon—seemed to point to the imminent possibility of invasion, sometime between September 8 and 10. “It seemed certain that the man was going to try,” Churchill said.

Those with even a little imagination and knowledge of the brutality the Nazis were capable of turned their minds to more desperate thoughts as the invasion threat grew more real. Leonard Woolf, a left-leaning Jewish intellectual and husband of the writer Virginia Woolf, secured a dose of poison to use if necessary to avoid the torture he knew would be their fate if they fell into Nazi hands. (As he would later discover, both he and Virginia were indeed on the Gestapo’s arrest list.) Churchill, with his much greater natural pugnacity but with equally suicidal grimness, said he planned to use the slogan, “You can always take one with you.”

In late June, Churchill sent a memo to Maj. Gen. H. L. Ismay, his representative on the Chiefs of Staff Committee, urging under greatest secrecy that mustard gas and other chemical weapons be readied for use on the landing beaches, as a last resort.

“We,” he said simply, “were prepared to go all lengths.”

On the same day work began on organizing the underground army. Ismay was apparently one of several British officials who all had the same thought at the same time. “It is essential to instill into the civilian population a thoroughly offensive spirit and a determination to attack the enemy by every means in their power, even after he may have succeeded in occupying some of our territory,” Ismay had explained a couple of weeks earlier. “Action by the civilian population in subjugated areas,” he suggested, had the potential “to give the enemy an immense amount of trouble.”

Recalling how effective Irish underground fighters had been in tying down the British forces during the “troubles” in 1920–22, Ismay suggested a study be made of their methods and tactics:

Our object would be to keep the enemy continually on the jump as we were in Ireland during that period. There seem to be three main roles: (1) Intelligence. (2) Sabotage. (3) Assassination…. We should have a nucleus who would presumably disappear into the civilian population when the tide of battle moved forward across them. Selected characters should be trained in the use of the pistol and the hiding of weapons. The same sort of man could be valuable for sabotage work, but he must be trained in carrying out his job so that it appears as much like an accident as possible.

Another man who had been thinking along the same lines was Peter Fleming, a young captain of the Grenadier Guards known for his intrepid travel adventures, his flippant, patrician air, and his impeccable turnout in immaculate breeches and highly polished riding boots. He was tall, slim, rich, and famous for his published accounts (in the Times and in several best-selling books) of his adventures: exploring the Brazilian Amazon, trekking 3,500 miles from Peking to Kashmir. (He would later be even more identifiable as the brother of Ian Fleming, the creator of James Bond.)

The start of the war found Fleming serving on the staff of a small, cryptically named unit in the War Office—MI(R), which stood for “military intelligence (research).” In fact, its brief was to study guerrilla warfare tactics. With Fleming at MI(R) was Major Gubbins, a decorated veteran of the Great War. He was 43, and shared with Fleming a penchant for travel and being well dressed, but in most other ways was a contrast. A colleague described him as a “small wiry little Scotsman”; another as “a real Highland toughie, bloody brilliant.” Pushy and tenacious, Gubbins had already produced three soon-to-be-classic training manuals for Allied partisan fighters—Partisan Leader’s Handbook, The Art of Guerilla Warfare, and How to Use High Explosives.

In late August 1939, Gubbins was sent to Poland as chief of staff of the British Military Mission, with the secret assignment of assisting the Poles and Czechs with the organization of anti-Nazi guerrilla forces. A week later he and the rest of the British embassy staff in Warsaw were fleeing the oncoming German blitzkrieg; Gubbins eventually made his way to Romania, where he obtained a false passport, slipped out of the country, and returned to England. During the ill-fated Norway campaign, he led several British special forces units that planned to use fishing trawlers to carry out hit-and-run attacks on German supply lines. But British forces were withdrawn before Gubbins’s commandos could come into action.

Within days of Ismay’s proposal, Fleming was on his way to southeastern England to begin organizing and training the underground force. Gubbins was named to command the operation. Seeking a name that would “cover a multitude of possible lines of action and wouldn’t create too much suspicion,” Gubbins decided to call his new secret army of British guerrillas “Auxiliary Units.”

Kent and Sussex, the English counties that stood on the coast to the south and southeast of London, were the most likely targets for the German landings. Hastily dispatched there with barely any instructions on how to proceed, Fleming decided that even before he began recruiting and training his men he had better put some stopgap preparations in place. Rounding up a supply of empty metal milk cans, he filled them with explosives, attached fuses, loaded them onto trucks along with crates of guns, bullets, and food, and drove around the countryside dropping them off with somewhat haphazardly chosen residents.

A remarkably diverse range of characters began to fill the Auxiliary Units. As David Lampe noted in his book The Last Ditch, while most of the officers were old-boy-network patricians of Fleming’s stamp, more than a few locally notorious smugglers and poachers joined the ranks, alongside well-to-do farmers, country doctors, gamekeepers and fishing guides, masters of foxhounds, shepherds—all men extremely familiar with local geography. Many of the initial recruits for the Auxiliary Units were stripped from the ranks of the Home Guard—much to the outrage of local commanders whose best soldiers kept disappearing without explanation. But Gubbins would pave the way by calling on the senior commanders and explaining that he had the power to take any men he wanted, whether they liked it or not; would they, accordingly, identify their most able and experienced men, preferably those who had served in the First World War?

“We were all people with confidence who wouldn’t get upset in an emergency and could cope with problems at critical moments,” recalled Eric Johnston, a 32-year-old farmer who had been tapped from the Home Guard to serve in an Auxiliary Unit in Ashburnham, East Sussex.

Absolute secrecy was enforced from the start. Most recruits did not even tell their families of their role until long after the war was over: for decades, the wife of one farm laborer who served in an Auxiliary Unit was convinced that her husband had been sneaking out to see another woman several nights a week during the war. But as Gubbins’s officers explained to their men, their lives as well as the lives of their loved ones could very well depend on their families literally knowing nothing of their activities that could be revealed to the Germans.

Recruits sent for training at Coleshill, a Palladian manor house about 80 miles west of London that Gubbins was able to commandeer for his headquarters, were told to report to the village post office in the nearby town. The postmistress would peer at their ID cards, duck into the back to make a phone call, and return saying only, “Somebody’s coming to fetch you.” Then she would studiously ignore the new arrival, refusing to answer any of his questions until a car came to whisk him away.

Much of the practical training focused on learning to move in absolute silence at night. (The poachers and smugglers had a head start here.) To practice during the daylight hours, they wore heavy dark goggles while the trainers observed them. The curriculum also included preparing and setting off charges of plastic explosives, using Thompson submachine guns and high-velocity sniper rifles, improvising booby traps (a training manual advised, “with a little imagination dozens of ideas will present themselves…the essential point is that for outdoor booby traps you must aim at killing by splinters—not by blast”), and familiarization with an array of secret sabotage weapons, including small mines disguised as lumps of horse manure that could burst the tires of a passing vehicle. Trainees were instructed on the vulnerable points of airplanes, tanks, trucks, and railroad tracks, and were expected to be able to answer hundreds of unusual exam questions:

If four pounds of charge is sufficient to fell a beech, what charge would be sufficient to fell a spruce of the same thickness?

How would you find True North at night without a compass?

Why carry gelignite in waterproof wrappings?

What would you do if one of your section developed hysteria?

How would you try to prevent being followed by dogs?

Each recruit was issued a rubber truncheon, a garrote, and a Fairbairn-Sykes Commando knife. The text at Coleshill for the section on silent killing was a booklet written by Capt. W. E. Fairbairn himself to accompany the stiletto-like knife he invented, which became standard issue to all Allied special forces in the war.

The basic idea behind the Auxiliary Units was to tie down the advancing German forces long enough to buy time for regular British army forces to concentrate and counterattack: no one expected a few thousand guerrillas, however well trained and equipped, to hold out very long against the Nazis. Initial estimates in fact put the life expectancy of the Auxiliary patrols in weeks, if not days—or even 24 hours. In later years, veterans of the force matter-of-factly recounted their complete willingness to carry out their tasks with utter ruthlessness— blowing up targets even if British civilians would be killed, assassinating collaborators, even killing their wounded comrades so they could not be captured and tortured for information by the Germans. “It was agreed you never left anyone behind,” recalled farmer Charlie Mason. “We’d kill him and then booby trap the body. We were told all this before we signed on.”

To reap the maximum benefit, the cells needed to be concentrated where they could do the most damage during the very first phases of the German landings, when the invader was most vulnerable and the element of time the most crucial: in a thin strip within 30 miles of the coast. British planners intended the hit-and-run attacks by the stay-behind fighters to dovetail with a larger mobilization of civilian resistance that would avoid the debacles that hastened the collapse of Poland and the Low Countries. A leaflet entitled If the Invader Comes: What to Do— and How to Do It was sent to every home in Britain:

When Holland and Belgium were invaded, the civilian population fled from their homes. They crowded on the roads, in cars, in carts, on bicycles and on foot, and so helped the enemy by preventing their own armies from advancing against the invaders. You must not allow that to happen here. Your first rule, therefore, is:

  1. If the Germans come by parachute, aeroplane or ship, you must remain where you are. The order is “stay put.”

The leaflet went on to encourage civilians to keep watch and report enemy movements, avoid spreading rumors, and above all to prepare for a kind of total—if passive—resistance:


“Think Before You Act,” the leaflet concluded. “But Always Think of Your Country Before You Think of Yourself.”

Having the larger civilian population “stay put” was also essential to allowing the Auxiliary Units to melt into the landscape as the German forces swept through.

By the end of July 1940, Fleming and Gubbins had worked out the basic operational structure for the guerrilla units. Patrols would consist of a leader and six men. They would operate with almost complete autonomy to safeguard the organization; no patrol would even know the identity of other members, so they could not be infiltrated or betrayed (as would later occur time and again, and with devastating consequences, to the French Resistance).

Gubbins’s studies of guerrilla organizations had convinced him that many were exposed and destroyed because it was too easy to trace the men back to their homes and their normal life. So his idea was that the instant the invasion began, Auxiliary Unit members throughout the country would simply vanish: they would move into prepared hideouts provisioned ahead of time with food, water, and weapons; wait for the Germans to pass by; and then emerge each night to wreak what havoc they could on the enemy’s rear.

Within weeks, hundreds of ingeniously concealed underground hideouts were carved out of the earth underneath woodlands, sheep pastures, brickyards, rubbish piles. A main room, often covered with an arch of corrugated steel, typically 20 feet long by 10 feet wide, held bunks and cases of food and explosives; a side room was fitted with a chemical toilet and cooking stove.

An array of imaginative devices concealed the hideout entrances, which were usually vertical shafts. A rectangular trapdoor was built into a sheep-feed trough; a half-ton tree trunk was mounted on a concealed underground hinge and counterbalance that could swing aside to reveal the opening; a gardener’s glass-covered cold frame, complete with growing cucumbers, covered more than one hideout entrance. In Wales and Northumberland, long-forgotten mines were pressed into service; in Scotland, dome-shaped, rock-lined underground dwellings constructed 2,000 years ago by the Picts served the purpose. By war’s end, some 1,000 hideouts had been built. (While most were later destroyed, a few remnants can still be found, and were cataloged by archaeologists of the Defence of Britain Project in the late 1990s.)

The invasion, of course, never came. But it was only after the Allies had secured the French coastlines following the D-Day invasion in June 1944 that the threat of a German landing finally receded for good. The Auxiliary Units had one more assignment before then, however: fearing that the Germans might respond to D-Day with a counterstrike against the Isle of Wight, several patrols were sent there in May 1944, prepared to open a behind-the-lines front to keep the Germans occupied while the D-Day landings proceeded.

The force was officially disbanded in November 1944. A few members of Britain’s never-to-be resistance movement joined special forces units in the regular army. But most recognized that, given their peculiar training, “we weren’t even of any use as soldiers,” as one Auxiliary Unit member recalled, adding that they didn’t even “know how to salute.” At the end of the month they all received a letter from their commander thanking them for their dedication to “a job which would require more skill and coolness, more hard work and greater danger than was demanded of any other voluntary organization”—and regretting that “in view of the fact that your lives depended on secrecy no public recognition will be possible.”

Would the Auxiliary Units have been a decisive force in Britain’s final days? Churchill himself took the keenest interest in the underground army, insisting on seeing weekly reports on its progress and making sure that first priority for new weapons went to them. But he also once observed that “wars are not won by heroic militias.”

Churchill was confident that as long as the Royal Air Force commanded the air and the Royal Navy the sea, an initial German landing would have faltered on attempts to land a second wave and maintain supply lines across the Channel. A war-game exercise by the Royal Military Academy Sandhurst in 1974 reached the same conclusion: though the Germans would almost surely have been able to secure a significant beachhead, they would have been cut off by the Royal Navy and ultimately defeated before they could cross the main defensive line of pillboxes and antitank barriers erected to protect London.

But that would not have diminished the crucial need to buy time with as bloody an initial resistance on land as possible: to force the Germans to expend their ammunition and supplies, and to prevent a dash to London that could have spread panic and collapse. “I have often wondered what would have happened if two hundred thousand German storm troops had actually established themselves ashore,” Churchill later wrote. “The massacre on both sides would have been grim and great. There would have been neither mercy nor quarter.” There is little doubt that Churchill’s secret army would have played a prominent part in that grim and great massacre, and that it was more than prepared to carry out Churchill’s admonition to “take one with you.”

Originally published in the November 2008 issue of World War II Magazine. To subscribe, click here.