What If: Hitler Invades Great Britain

In the summer of 1940, Nazi Germany stood at the peak of its early-war triumphs. France had collapsed in six weeks, the Low Countries were occupied, and now Hitler looked across the English Channel with a conquering eye. Great Britain, stubborn and isolated, was now the last obstacle to Germany's total domination of Western Europe.

In our timeline, Britain held out against what became known as the Blitz, the air onslaught the Nazis launched against the island. Yet, the RAF held firm, helped by a German strategic miscalculation. Yet, the Germans had Operation Sea Lion on the drawing board if things had gone differently. 

If Germany had been so bold as to invade Britain, it would've had to win the Battle of Britain.

Bombing the Wrong Target

The Battle of Britain was a prerequisite for a potential German invasion. The Luftwaffe’s task was simple in theory: crush Fighter Command, gain control of the Channel, and expose southern England to invasion. For a time, Germany came dangerously close.

Through August 1940, airfields such as Kenley, Biggin Hill, and Tangmere sustained repeated hits. Radar stations were damaged or forced offline. Pilots were exhausted. Replacement aircraft came off the line as fast as factories could assemble them. Had Germany continued this pressure for several more weeks, Fighter Command might have been forced to retreat further north. 

German Heinkel He 111 formation. These bombers were used during the Battle of Britain.

However, the Luftwaffe did indeed focus early attacks on RAF airfields, putting southern England’s bases under significant duress. Most of these airfields, however, were rudimentary, often dirt strips, and could be repaired within 24 hours, minimizing long-term disruption. 

A critical factor in the battle was a misestimation on both sides. German intelligence consistently underestimated the number of operational RAF fighters and available pilots, while British intelligence overestimated German strength. This created a persistent illusion. Germany believed it was on the verge of victory, while Britain felt it was barely holding on. In reality, British fighter production and pilot availability increased steadily throughout the battle, outpacing German losses in both quantity and quality.

Aircraft Production and Attrition

Battle of Britain attrition statistics highlight the strategic imbalance:

Month	British Production	German Production
June	446	164
July	496	220
August	476	173
September	467	218
October	469	200
Total	2,354	975

Air Chief Marshal Sir Hugh Dowding began the battle with roughly 600 operational aircraft, while the Luftwaffe deployed around 750 serviceable bombers, 250 dive-bombers, and over 600 single-engine plus 150 twin-engine fighters, organized in three air fleets. Despite intense attacks, German intelligence consistently overestimated the damage inflicted. 

An air observer during the Battle of Britain.

Fighter Command airfields suffered only minor, temporary disruption. Manston and Lympne were inoperable for a few hours, while radar stations were largely spared (while some stations were put offline, the Chain Home network remained intact). By late August, Luftwaffe estimates claimed Fighter Command’s first-line strength had halved, but Dowding still commanded roughly twice that number, and British production continued to outpace attrition.

Over the course of the battle, RAF fighter strength rose from 644 to 732 aircraft, while German fighter strength fell from 725 to 275. Losses of trained personnel were similarly imbalanced. The RAF killed or lost 104 pilots in mid-August, versus 623 Luftwaffe airmen (killed or captured) during the same period. These statistics illustrate that, despite appearances, the RAF was winning the battle of attrition.

British Strategic Options

Many narratives assume Britain had no choice but to defend airfields as they did. This was not strictly true. The RAF could have relocated bases further north, beyond the range of German escort fighters, and conserved strength while the Luftwaffe exhausted itself. 

Instead, Britain chose forward defense, seeking to inflict maximum damage on the Luftwaffe and to protect as much of the island as possible. A more northerly defensive posture might have reduced immediate airfield losses while increasing civilian casualties from bombing, but would have preserved British fighter strength for a prolonged campaign. 

The Consequences of Luftwaffe Miscalculations

By August 24, 1940, the Luftwaffe was trying to target RAF airfields and oil tankers in East London when they strayed off course and bombed residential areas. In response, Churchill ordered retaliatory strikes on Berlin, which provoked Hitler into forcing Goring to switch the strategy from targeting the RAF to targeting towns and cities.

View down the River Thames toward smoke rising from the London docks after an air raid during the Blitz.

While this relieved some pressure on Fighter Command, the Luftwaffe was already losing aircraft and pilots faster than Germany could replace them, whereas the RAF was steadily replenishing both. 

For an invasion of Britain to succeed, Germany would have needed:

1. Eliminating or sealing off Royal Navy forces from the landing and approach areas.

2. Eliminating the Royal Air Force.

3. Destroying all Royal Navy units in the coastal zone.

4. Preventing British submarine action against the landing fleet.

   
   

None of these conditions was anywhere near achievable. The combination of robust British production, resilient air defense, and naval superiority meant that Germany lacked the capacity to defeat the UK outright. But for this article, let's say they create the conditions favorable to launching an invasion.

Operation Sea Lion

With air superiority achieved in this alternate path, Operation Sea Lion becomes a possibility, albeit one that’s still far-fetched. 

Sea Lion was an improvised operation. Germany lacked proper landing craft and instead converted nearly 2,000 river barges into makeshift troop transports. These barges were slow, flat-bottomed, and vulnerable to waves, mines, and naval gunfire. 

Still, the plan existed as follows: 

• Cross at the Dover–Calais narrows.

• Land between Folkestone and Hastings.

• Insert airborne troops behind British coastal defenses (The eastern coast of England, between The Wash and the River Thames, but in more refined plans, the coast of Kent and Sussex in Southern England.)

• Capture a usable port and push inland (Dover).

• Rely on the Luftwaffe to keep the Royal Navy out of the Channel.

German plans for Operation Sea Lion and the invasion of Britain.

Though Raeder warned Hitler that the Kriegsmarine could not guarantee proper protection for even one day, air superiority dramatically reshapes this equation. Stukas and Ju 88s—unopposed by fighters—would devastate British ships approaching the invasion corridor. But it's hard to imagine that they would be unopposed by the RAF. And then there's the British Navy.

The Royal Navy: Britain’s Southern Shield

The greatest danger to the Sea Lion was not only the RAF but also the Royal Navy. 

Even after evacuating Dunkirk, Britain still possessed a strong fleet compared to the Kriegsmarine: 

Type	Royal Navy (June 1940)	Kriegsmarine (June 1940)
Battleships	15	0 operational
Aircraft carriers	7	0
Cruisers	66	9 (3 H, 6 L)
Destroyers	176	22
Submarines	60	57
Torpedo boats	39	27
Fast attack craft	30 MTBs	24 S-Boats

In our world, the RAF ensured the Home Fleet could operate with relative freedom. In the alternate scenario, with the RAF further north, it would mean longer operational windows to maintain air cover over the channel. But the British were also actively fortifying the southern coast. 

Britain’s Coastal Defenses

Britain did not wait passively. The southern coast was reinforced heavily throughout the summer of 1940:

Sector	Responsible Division	Infantry Brigades	Artillery	Engineers	Mobile / Counterattack	Home Guard
Beach B (Folkestone → New Romney)	45th Division	134th & 135th	61st & 58th Fd Regts + local coastal batteries	264th & 265th Fd Cos RE	1st Armoured Division elements held inland	Kent Home Guard (Brenzett, Brookland, Dymchurch, Lydd, New Romney)
Beach C (Rye → Hastings)	55th Division	164th & 165th	75th & 114th Fd Regts + coastal batteries	201st & 202nd Fd Cos RE	29th Independent Brigade Group & attached light armour	East Sussex Home Guard (Rye, Hastings, Fairlight)
Beach D (Bexhill → Eastbourne)	12th Division	35th & 36th	70th Fd Regt + coastal batteries	203rd & 204th Fd Cos RE	Limited; corps reserve	Bexhill, Crowhurst, Pevensey battalions
Beach E (Beachy Head → Brighton)	48th Division	143rd & 144th	71st Fd Regt + 1–2 coastal batteries	205th & 206th Fd Cos RE	Light armour behind Brighton; limited	East & West Sussex Home Guard
Dover / Ramsgate / North Kent (including Dover approaches)	Dover Fortress / 44th (Home Counties) Division	Dover Fortress units + 131st & 132nd Bdes	Dover heavy batteries + 57th & 58th Fd Regts	560th–562nd Fd Cos RE	Minimal; local counterattack only; some 1st Armoured elements held inland	Dover, Deal, Ramsgate, Margate, Sandwich Home Guard
Isle of Wight / Hampshire Coast	48th (South Midland) Division / Portsmouth Fortress	Hampshire Regiment & Royal Sussex Regiment battalions	Portsmouth & Isle of Wight coastal batteries	48th & 49th Fd Cos RE	Light armoured / Royal Marine mobile battalion held inland	Isle of Wight & Hampshire Home Guard

These defenses would have had to contend with a German first wave consisting of 13 infantry and mountain divisions, 2 airborne divisions, and the special forces of the Brandenburg Regiment. The second wave would consist of 8 panzer and motorized infantry divisions, with a third wave of 6 infantry divisions.

These defenses were never meant to stop an invasion outright. They were designed to delay it—long enough for counterattacks to form. If the Germans land intact and capture a major port, they would have to hold these gains until more reinforcements and supplies could be brought across the channel.

Could Sea Lion Have Succeeded? 

Scenario 1: A German Foothold

If Germany:

• Suppresses Fighter Command (I don't think they could destroy it)

• Suppresses the Royal Navy with airpower

• Lands most of the first wave

• and captures Dover or Folkestone

  
  

…then the Wehrmacht could begin pushing toward London with support from a second wave.

German early-war infantry was tactically superb, battle-tested, experienced, and well-led. British regular units were brave but recovering from Dunkirk; many formations lacked adequate training or equipment.

This scenario ends with a bitter, weeks-long urban battle for London. Germany could win if somehow everything went its way, but I find this highly unlikely. Even if they gain a foothold, the channel crossing would remain contested along with the beachheads.

Scenario 2: Battle for the Channel

The Germans would most likely have planned a daytime landing in the early morning hours. With the plan intended for September, the weather in the English Channel at this time was highly variable. This could make the German crossing on barges quite perilous, depending on the weather. Add in an interdicting Royal Navy and RAF battling the Luftwaffe and supporting Kriegsmarine forces, the English Channel would devolve into chaos.

I could see maybe some of the airborne or special forces landing on the island. But without follow-on troops, they would no doubt be hunted down, cornered, and captured or killed. Thus, the invasion would most likely be decided in the channel before the first German troops set foot on shore. Add possible nighttime air or sea raids against the invasion barges on the eve of the British invasion (which the RAF did in our timeline). If successful, these raids could diminish the Germans' seaborne lift and force them to scrap the operation.

For the United States

Britain’s fall or partial occupation with an active insurgency/resistance would transform American strategy. Roosevelt loses:

• A friendly staging ground.

• An Atlantic bastion.

• The most persuasive argument for intervention.

  
  

Isolationist political forces would surge on the home front, but that pressure would not deter FDR. He could counter these notions by highlighting how the threat is that much closer to US shores.

Strategically, Iceland, Canada, and Greenland all become more important. To regain a foothold back toward Europe, the US would have to deploy more carriers to the Atlantic in support of an "island hopping" campaign from Iceland to Ireland, then on to the British Isles to retake them in the wake of Pearl Harbor (who knows if Germany would continue to take territory west or if it would purely focus on the USSR).

A depth charge exploded during the Battle of the Atlantic. Note the merchant vessel on the horizon to the left.

The Battle of the Atlantic would become even more crucial, for with British ports serving as a staging ground for the Kriegsmarine U-Boat fleet and airfields for the Luftwaffe, the US Navy would have quite the challenge before it to open a pathway to retake Britain. During this time, the US, using submarines, would probably try to keep any British resistance alive until the island could be liberated. But all of this would take time for the US would have to build up its naval forces to support expanded operations in the Atlantic as well as what's required to fight the Japanese in the Pacific.

Lastly, support for the USSR would become even more crucial. All of this would greatly upset the timeline as we know it, for Stalin demanded a second front. With a degraded Britain, would the US opt to invade North Africa still? With the Home Islands under occupation, that doesn't make North Africa irrelevant, for the Suez Canal is still crucial to hold. But the plan for Operation Torch and the forces available would change, given that part of the invasion came from Britain, which would now be under occupation.

For the Soviet Union

With the British Home Islands partially or fully occupied, Germany may take this opportunity to shift its focus east. While a resistance and insurgency would hold down forces in the west, Germany would still have the capacity to launch an Operation Barbarossa. As the pressure from such an operation mounts, the Battle for the Atlantic (which shifted with German control of southern Britain), Stalin would still demand that the US take action to alleviate that pressure (North Africa may remain on the table, though its viability may be called into question).

An American Douglas A-20 bomber lifted onto a vessel filled with Lend-Lease materiel.

The Lend-Lease route through Iceland to the USSR would become even more contested, perhaps forcing the US to provide more resources via Alaska. This would make the Aleutians more strategically important (which the Japanese seized in 1942). As such, Moscow's survival would become that much more dire. Would Stalin let US troops join his forces to stop a German invasion of the Russian heartland? If I had to guess, probably not, but it's an interesting thought.

Final Thoughts 

Operation Sea Lion was an ambitious plan, but Germany’s lack of a naval force to lift its armies across the English Channel was a major obstacle. Göring consistently overpromised the capabilities of the Luftwaffe (as we saw at Dunkirk and during the Battle of Britain), and Raeder even said he could not guarantee safe passage in the English Channel for more than a day.

Even if the Luftwaffe were able to keep the pressure on Fighter Command in the south and force them to retreat, getting across the channel and keeping their forces supplied would be difficult with a Royal Navy that would no doubt sortie against any invasion fleet. 

Thankfully, history did not go down that path.

Sources

Books & Official Histories

1. Bungay, S. (2001). The most dangerous enemy: A history of the Battle of Britain. Aurum Press.

2. Collier, B. (1957). The Defence of the United Kingdom (Official History). London: HMSO.

3. Dobinson, C. (2001). Beaches, Fields, and Ditches: The Anti-Invasion Defences of Britain 1940–1941. London: Council for British Archaeology.

4. Ellis, L. F. (1954). The War in France and Flanders 1939–1940 (History of the Second World War, United Kingdom Military Series). London: HMSO.

5. Holmes, R. (2005). Britain’s Beaches in 1940: The Anti-Invasion Preparations. London: HarperCollins.

6. Hughes, M. (1990). British Divisions 1939–1945. Ramsbury: Crowood Press.

7. Kennedy, D. M. (1999). Freedom from fear: The American people in depression and war, 1929–1945. Oxford University Press.

8. Macksey, K. (1976). Invasion: The German Invasion of England, July 1940. London: Panther Books.

9. Murray, W., & Millett, A. R. (2000). A war to be won: Fighting the Second World War. Belknap Press.

10. Overy, R. J. (2013). The Battle of Britain: The myth and the reality. W. W. Norton.

11. Roskill, S. W. (1954). The war at sea, 1939–1945: Volume I. Her Majesty’s Stationery Office.

12. Weinberg, G. L. (1994). A world at arms: A global history of World War II. Cambridge University Press.

    
    

Web / Online Sources

1. Everything Explained Today. (n.d.). 31st Infantry Brigade (United Kingdom). Retrieved November 18, 2025, from https://everything.explained.today/31st_Infantry_Brigade_%28United_Kingdom%29

2. Romney Marsh History. (n.d.-a). Auxiliary Units / Stay-Behind Patrols. Retrieved November 18, 2025, from https://romneymarshhistory.co.uk/auxunits

3. Romney Marsh History. (n.d.-b). Resistance and Home Guard Units in Romney Marsh. Retrieved November 18, 2025, from https://romneymarshhistory.co.uk/resistance

4. StayBehinds.com. (n.d.). Snargate Patrol. Retrieved November 18, 2025, from https://www.staybehinds.com/patrol/snargate-patrol

5. Wikipedia contributors. (n.d.-a). 264th (Sussex) Field Company, Royal Engineers. Retrieved November 18, 2025, from https://en.wikipedia.org/wiki/264th_%28Sussex%29_Field_Company%2C_Royal_Engineers

6. Wikipedia contributors. (n.d.-b). Kent Fortress Royal Engineers. Retrieved November 18, 2025, from https://en.wikipedia.org/wiki/Kent_Fortress_Royal_Engineers

7. Woolmer Forest Heritage. (n.d.). The Anti-Invasion Landscapes of England 1940. Retrieved November 18, 2025, from https://woolmerforest.org.uk/E-Library/B/Beaches%20fields%20streets%20and%20hills%20-%20the%20anti-invasion%20landscapes%20of%20England%201940.pdf

National Archives / Primary War Diaries

1. The National Archives (UK). (1940-a). 45th Division War Diary, 1940 (WO 166/422). Kew, London: The National Archives.

2. The National Archives (UK). (1940-b). 55th Division War Diary, 1940 (WO 166/566). Kew, London: The National Archives.

3. The National Archives (UK). (1940-c). Dover Fortress War Diary (WO 166/1430). Kew, London: The National Archives.

4. The National Archives (UK). (1940-d). Portsmouth Defence Scheme (WO 199/1788). Kew, London: The National Archives.

5. The National Archives (UK). (1940-e). Romney Marsh & Royal Military Canal Defence Scheme, 1940 (WO 199/1787). Kew, London: The National Archives.

6. The National Archives (UK). (1940-f). South Eastern Command Defence Plans (WO 199/1801). Kew, London: The National Archives.

7. The National Archives (UK). (1940-g). XII Corps War Diary, July–October 1940 (WO 166/1077). Kew, London: The National Archives.

Images

1. Bundesarchiv. (n.d.). Übungen mit Panzer III für Unternehmen Seelöwe [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Bundesarchiv_Bild_101II‑MW‑5674‑45,_%C3%9Cbungen_mit_Panzer_III_f%C3%BCr_Unternehmen_Seel%C3%B6we.jpg

2. Unknown author. (n.d.). Heinkel He 111 during the Battle of Britain [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Heinkel_He_111_during_the_Battle_of_Britain.jpg

3. Unknown author. (n.d.). Battle of Britain air observer [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Battle_of_britain_air_observer.jpg

4. Unknown author. (n.d.). London Blitz, 7‑9 September 1940 [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:London_Blitz_791940.jpg

5. Unknown author. (n.d.). Operation Sea Lion map [SVG graphic]. Wikimedia Commons. https://en.wikipedia.org/wiki/Operation_Sea_Lion#/media/File:OperationSealion.svg

6. Unknown author. (n.d.). Depth charge explosion during the Battle of the Atlantic, c. 1943 [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Depth_charge_explosion_during_Battle_of_the_Atlantic_c1943.jpg

7. Unknown author. (n.d.). Lend‑Lease bomber [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Lend_Lease_Bomber.jpg