US invasion of the U.K. Military Geography

Yun-shuno

Banned
Okay so I am not as interested in the politics that makes this scenario possible, but how it would be achieved if the conditions for it occurred. Say the US and UK are at war for whatever reason or maybe the Nazis and conquered the country or there has been a communist revolution.

From a military standpoint how would one invade the UK from the west? Down from Iceland? Up from the southwest coast. Island hop from Ireland to Wales?

Basically I'm asking if the US invaded the UK what would the invasion arrows look like on a map and why?
 

shiftygiant

Gone Fishin'
The US and her Allies cut Britain off from trade to starve Britain until she surrenders. Then occupation troops take control of major cities as part of the peace agreement.
 
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shiftygiant

Gone Fishin'
That wasn't what I was asking.
Well that's what would happen. The US lacks any staging ground to invade the UK, and the closest would have been immedietly seized, rendered ineffective, or defended against by the UK. Starving the country to surrender is the only realistic option the US can take in such a hypothetical.
 
That wasn't what I was asking.

So you want a specifically liberation assault?

See as Shiftygiant has pointed out in a US-UK war the sensible option is blockade which is difficult given USN versus RN naval ratios until the late 1930s but becomes much easier even without a Second World War from 1940 onwards.

Now a liberation assault works by different rules and a lot would depend on whether the occupier of Great Britain had also successfully occupied Ireland?
 
Well that's what would happen. The US lacks any staging ground to invade the UK, and the closest would have been immedietly seized, rendered ineffective, or defended against by the UK. Starving the country to surrender is the only realistic option the US can take in such a hypothetical.

I doubt its realistic to think the US stop sea traffic across the Dover Narrows, indeed I imagine the Channel from Portland in the south to the Thames estuary would be defended almost air tight given the resources at Britain's disposal so starving her out isn't an option.
 

shiftygiant

Gone Fishin'
I doubt its realistic to think the US stop sea traffic across the Dover Narrows, indeed I imagine the Channel from Portland in the south to the Thames estuary would be defended almost air tight given the resources at Britain's disposal so starving her out isn't an option.
Well yes, but again this would also require Britain to be allied with France and/or Belgium who are willing to support Britain, which is more than likely. Starving Britain out is really the only way I can see getting over the issue of Britain's defense potential.
 

Yun-shuno

Banned
Well that's what would happen. The US lacks any staging ground to invade the UK, and the closest would have been immedietly seized, rendered ineffective, or defended against by the UK. Starving the country to surrender is the only realistic option the US can take in such a hypothetical.
Could they not invade from the coast somewhere and push down southeast from there?
 

shiftygiant

Gone Fishin'
Could they not invade from the coast somewhere and push down southeast from there?
They would need a staging ground, so France would presumably be Allied with America, an area that is either not defended or weakly defended, given what is on the South and Southeast coast, both geographically and population wise, is an extremely tall order, and the capabilities to bring the necessary supplies to sustain their forces, which would require the capture of ports, which would be heavily defended, or scuttled the moment the stars and stripes were in sight.

Assuming France is allied, then simply blockading Britain is by far the most simple and elegant solution.
 

Yun-shuno

Banned
They would need a staging ground, so France would presumably be Allied with America, an area that is either not defended or weakly defended, given what is on the South and Southeast coast, both geographically and population wise, is an extremely tall order, and and the capabilities to bring the necessary supplies to sustain their forces.

Assuming France is allied, then simply blockading Britain is by far the most simple and elegant solution.
An amphibious assault is not possible?
 

shiftygiant

Gone Fishin'
An amphibious assault is not possible?
It's possible, but like the unmentionable seamammel, it's not really that viable a solution. Perhaps in small, tiny cases like sabotaging Southhampton and Portsmouth, but beyond it's not all that good an idea to send you're troops up through an area that will become one of the most defended spots of land on Earth the moment someone puts two and two together on why all these Americans are sitting in the Channel Ports.
 
An amphibious assault is not possible?

The problem is that given the geography of the British Isles a relatively small naval force can respond in strength to landings covering a large length of coastline. Meanwhile the internal communications of Britain are very dense allowing any point to be rapidly reinforced by land.

Note this is not the same as impossible but it does mean that the US would have to muster a considerable preponderance of force and the logistics resources to sustain them in combat.
 

Nick P

Donor
In the film It Happened Here the US liberation forces are shown as landing in Cornwall which doesn't ring true given the lack of landing beaches, ports or airstrips.

As always it's down to logistics. Looking at D-Day the challenge was to get lots of supplies and reinforcements ashore after the initial landings. That's why they had Mulberry Harbours built. If they'd been able to take Cherbourg or Antwerp early on life would have been so much easier. To capture even a minor port would be essential. You'd need to set up operational bases in nearby countries like Ireland and France or Belgium. Build up major supply depots and have factories produce locally. Picking off the small Channel Islands and the six counties of Northern Ireland would be the easy part.

Terrain wise you want large flat beaches for the landing craft and amphibs to run ashore onto. Cliffs are not fun as the Rangers at Pointe du Hoc will tell you. Most of these beaches are on the East coast which means going through the English Channel or around the north of Scotland. To do that you need to remove the enemy. Taking out all opposition means sinking the 50 warships (in todays numbers) of the Royal Navy including the highly trained and rather pesky Submarine Service. The RAF would take a lot of beating but once you've knocked out most of the 200 airfields that are available you can narrow things down.

You could invade Great Britain from NI but where do you land? You could aim for the port facilities at Cairnryan and Stranraer. From there you push out into the Galloway hills towards the A74/M74 (block this to complicate UK logistics and counter-attacks) and set up defences and build up for a major breakout. Air cover from NI is within range. But, and this is the big but.... This is a long way from anywhere important with few decent roads through tough terrain. You have to make the choice of going north to Ayr and Glasgow to take out Scotland or going east to Gretna for the main road north-south, the M6.

Invading from France is the standard sea-mammal exercise. You either aim for the South Coast or the Anglia coastline. Taking Harwich or Felixstowe alongside the large landing grounds of Essex and Suffolk helps with your resupply.

All of this has to take into consideration that today, all of the English and Welsh coast is within 2 hours drive of an army base. Back in the 1940s there were more railway lines which again, were within 2-3 hours of a military base. The density of the UK helps us in our defences.

Basically, I wouldn't want to try it without a seriously overwhelming invasion force.
 
If this is at the World War 2 level of development, it's likely that the United States could take Iceland, the Orkneys, the Shetlands, maybe Ireland. If so, even without taking Ireland (could be captured by the UK early on), then they'd be able to invest more resources in bombing Britain, more even than against Japan. I don't think they could resist an attack like that, and the US was always better at submarine warfare than the Germans, so a blockade could actually be maintained. This is while defeating the colonies in detail, and making incredible offers of post-war prosperity to the dominions.

After that, nuclear weapons would be used by the UK against an invasion, so nuclear weapons will be used tactically in response, so civilians in the UK will be killed by them, so a nuclear exchange could take place, or a coup could remove the UK government to surrender and avoid this.
 
Assuming its mid 1930s or later, the US would want the Azores and Iceland first, followed by Ireland as airbases and air ferry routes, as well as refueling and repair anchorages are needed. If before mid 1930s the air bases are less important but anchorages for refueling are still needed.

Then take the Isle of Man, some of the northern Scottish Islands and that opens up more options.

As to the invasion of Britain itself, I would feint at Liverpool but make the actual landing in the Glasgow area and as air superiority is vital for a successful invasion, this allows interdiction of rail lines leading from England to Scotland during the build up phase, provides for a good harbor on the Atlantic side of the island that is well within the range of air cover, and a good road network leading out. Although its hilly, those hills aren't as rugged as further north.

Main axis of attack into the English Midlands, saving London itself for the final stages. Secondary drive into the Scottish Highlands and into tertiary drive into Wales
 

Saphroneth

Banned
The first thing that has to be assumed in anything remotely credible is that there is no significant navy defending the UK. This is somewhat unlikely because of the Royal Navy - until post-WW2 it was aimed to be the equal first in power in the world, and anyone who managed to invade the UK despite that would need a powerful navy of their own (simply to overmatch the RN) or perhaps enough naval air power to be the equivalent of a couple of dozen aircraft carriers.

So there's a large navy defending the British Isles. What this in turn means is that you need to bring an overwhelming navy of your own - in the 1940s it is possible with UnRep to operate a large navy a couple of thousand miles from a base, but you'll probably need some convenient large base to operate from (Iceland? The Azores? Both are quite a long way off and Iceland is quite suboptimal).

But let's assume you do it. Now you need to get ashore.

The best place if you're coming from the west is probably Ireland - it exposes you to less in the way of air attacks and small-naval sorties which would otherwise harm your supply line (either up the channel, into the Irish Sea or past Scotland) from the many excellent UK ports. But you'll need to get over the Irish beaches, and also capture or bring along your harbour.
Only problem... the people who OTL invented the portable harbour are the people you're invading, and that couldn't cross oceans - while there's only a couple of really good ports on the Irish west coast (Limerick looks like the best).

Perhaps you should try landing on the west coast of Devon instead, but that's also bereft of large ports (I mean... Bude...) and the best port with that side of the UK as the approach is probably Bristol.
Which is to say, a port in the Severn. With one of the largest tidal ranges in the world.


It ain't easy.


I don't think they could resist an attack like that, and the US was always better at submarine warfare than the Germans, so a blockade could actually be maintained.
Honestly, that one I'm not sure of - the US was better against the Japanese than the Germans were against the British, once the torpedo problems were worked out. It's going to be hard for the US to blockade British-French or British-Dutch trade, as well...
 
There aren't many good invasion beaches in Ireland or the West of the UK. The US would need to seize a port like Cork and then build up air bases and deploy other forces the Irish road net even in the 1990's remained rudimentary compared to the UK; it wasn't until recently that road projects received serious investment (mainly by the EU).

The West of the UK has similar issues in that there are few suitable beaches in the South West or Wales, plus the road net in the 1940's was woeful consisting of one and two lane roads and rail both of which could be blocked with relative ease. Even in the 1960's the Motorway network was still limited west of Swindon and remained so until the 1970's by which time a lot more dual carriageways had been built. However, these still provided limited and easily blocked access to the rest of the UK.
 
If this is at the World War 2 level of development, it's likely that the United States could take Iceland, the Orkneys, the Shetlands, maybe Ireland. If so, even without taking Ireland (could be captured by the UK early on), then they'd be able to invest more resources in bombing Britain, more even than against Japan. I don't think they could resist an attack like that, and the US was always better at submarine warfare than the Germans, so a blockade could actually be maintained. This is while defeating the colonies in detail, and making incredible offers of post-war prosperity to the dominions.

After that, nuclear weapons would be used by the UK against an invasion, so nuclear weapons will be used tactically in response, so civilians in the UK will be killed by them, so a nuclear exchange could take place, or a coup could remove the UK government to surrender and avoid this.

The USN submarine force was more successful than the U-boats primarily because their enemy (the IJN) thought convoys happened to other people and the Japanese had done relatively little ASW work pre war and the Japanese Merchant fleet was already to small for its needs and this coupled with an inability to replace merchant losses allowed it to be dominated with far far less effort than was required in the Atlantic - and lets not mention the Mk14 debacle.

The U-boats on the other hand were initially up against the RN and Britain's merchant fleet + a large chunk of the rest of the world who had invented Anti Submarine Warfare and started off being good at it and then became very good at it and the USA who could replace more than what the U-boats could sink - so the Germans were up against it and still made the allies work hard for their victory

So no the US was not better at Submarine Warfare - but they did not have to be......

As for the rest of it - all a bit vague - when in WW2? - for example in 1939 the US Army (including its fortification artillery units) is smaller than the Belgium army and has a battalion of mixed obsolete tanks - in 1945 half the military stuff on the planet had been made in the USA in the preceding 5 years and its military was buff.

In OTL 1945 the Atom bomb was a collaborative effort - if the British are not involved then there is likely no ATOM bomb in 1945

To the OP - best way to invade the UK is from France / Belgium / Netherlands and attack into the Sussex (mostly West Sussex) coast line - the tried and tested route - basically a reverse Op Overlord - with the aim to head West capture Portsmouth and Southampton (the only major ports) in Hampshire ASAP.

Then after using the ports to build up forces - Capture London.

But soooo many problems with this approach - the British for one - and I cannot see this ever being a requirement unless Britain becomes like North Korea or something - then it would have come to terms or not required the invasion in the first place by seeking a political solution.

Again too much vagueness....
 
I mean if the war occurred pre-nuclear bomb, I would expect an American victory following blockade and strategic bombing, maybe ending with a nuclear bomb at some point. Britain would surrender before an invasion.

If France and the Low Countries were neutral but friendly to the USA, they might not trade with Britain openly. And I don't think that Britain could produce enough ships to keep up during a war of industry, so eventually they'd be cut off at sea. I don't believe Britain is likely to develop a nuclear weapon first; and even if they did, and even if they used it (probably against an invasion beachhead), the USA would not be all that far behind. If the War is progressing along the 1940's level of technology, I think the USA could tank bombs until they made one of their own, and then their industrial advantage comes into play again.
 
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