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Author Topic: Wargaming Sea Lion  (Read 4257 times)

besilarius

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on: July 17, 2019, 06:35:54 AM
Wargaming Seelöwe

Operation Sealion, or, in the original German Unternehmen Seelöwe, is one of the most famous “what ifs” of the Twentieth Century.

On July 16, 1940, following the collapse of France, the Dunkerque evacuation, and the rejection of his peace overtures, Adolf Hitler issued Führer Directive No. 16, which initiated preparations for an invasion of Britain.  At the time, it seemed to many that if Hitler had tried an offensive across the English Channel a defenseless Britain would inevitably fall.  But was it so?  What were Hitler’s chances? 

In 1973 historian Paddy Griffith, just beginning his career as an instructor at the Royal Military Academy Sandhurst, decided to evaluate the chances of a successful German invasion of Britain by using a wargame.

Organization. Griffith’s wargame was much more than a board with a set of counters, a rule booklet, and some dice.  It was a massive multiplayer game, which Griffith later wrote about in Sprawling Wargames.  Based on traditional kriegsspiel methodology, the game involved several dozen players and umpires, all isolated from each other except by means of simulated signaling.  Many of the players and umpires were veterans of the war from both sides.  Among them were former wartime senior German officers such as Luftwaffe fighter Generalleutnant Adolf Galland and Kriegsmarine Vice Admiral Friedrich Ruge, as well as several men from both sides who had been lower ranking offices and later risen higher, including Christopher Foxley-Norris, who had commanded a fighter squadron during the Battle of Britain and rose to air chief marshal, Sir Edward Gueritz, a junior naval officer at the time who became a rear admiral, Heinz Trettner, who had served on the staff of the German airborne forces in 1940, rose to command a parachute division by war’s end, and later served as Inspector General of the post-war German air force, and Glyn Gilbert, a junior officer in one of the defending infantry battalions in 1941, who later rose to major general.

Each side was given the same forces, operational plans, and intelligence as it had in 1940.  The game was based on the assumption that the Luftwaffe had still not won the battle for air supremacy over the Channel and southern England by the time the landings were scheduled to take place, in early September, which was in fact the case.  The intelligence picture greatly favored the British, who had proven much better at securing information about the enemy’s plans and force than the Germans had on their own.

 

German Background.  The German armed forces had earlier investigated the possibility of an invasion of Britain, an operation in which the Kriegsmarine had little faith, and the Army not much more.  Nevertheless, upon receiving their orders, the two services worked to cobble together an amphibious doctrine, improvise specialized equipment, and train troops.  Initially the landings were set for early August, but this was postponed, eventually to mid-September.  The Army seems to have envisioned the operation as something akin to a river crossing.  German-dominated Europe was scoured for 1,910 river barges, canal boats, and similar vessels that could quickly be adapted as "landing craft,” though many were underpowered or wholly unpowered, and would have had to be towed across the Channel.  Meanwhile, some tanks were modified to be able to “swim” a bit, in order to get them off landing barges and on to the beaches.

The German plan was to develop a minefield screen blocking the English Channel from intervention by the Royal Navy, after which assault forces would begin crossing from bases on the European coast, bound for several landing sites, while airborne forces would secure positions behind the beaches in order to cover the landings.  There were two plans, one for landings on the east coast of England, and one for landings on the southeastern and southern coast.  The assumption was that once ashore the ground forces would quickly break the back of British resistance.

Although the Germans had available about 27 divisions plus some independent formations, the first wave only comprised elements of about nine infantry or mountain divisions, one panzer division, and two airborne divisions, plus some minor formations. And these forces would not be very mobile.  The Germans relied rather heavily on horses, and planned to land about 4,500 in the first wave and about 19,000 more over the next two days of the invasion.  In addition, at best they were only going to land about 250 tanks during the first few days of the invasion, mostly modified Panzer II and Panzer III models, with only about 40 Panzer IVs.  Follow-on forces totaled 15 more divisions, including more panzer formations.  The total manpower committed to the operation was about 330,000 ground troops.

The Germans would, of course, be greatly superior in the air, but operating at considerable range from their bases.  At sea, the situation of the German Navy was very poor, with virtually no major warships, even destroyers being in very short supply.

 

British Background.  The British established a series of "Stop Lines,” each manned by the Home Guard (of whom there were nearly a million men enrolled, albeit poorly equipped and ill-trained) and some regular troops holding improvised positions on defensive terrain.  Their mission was to delay the invaders until stronger forces could arrive from reserve positions to undertake counterattacks.  Although badly hurt by the massive loss of equipment during the campaign in northwestern Europe and the Dunkerque operation, by the end of August the British Army had been mostly re-equipped with arms procured abroad or through ramped-up domestic production.  There were some 25 divisions plus several independent brigades.   About 17 divisions were more or less fully equipped, including two armored divisions.  The defending forces included the 1st Canadian Division (the most well-prepared division available, full strength and fully equipped, though without combat experience), plus the less-well prepared 2nd Canadian division and partial divisions from Australia and New Zealand.  Less mobile divisions were largely assigned to backstop the stop lines.  The principal strike forces, in GHQ Reserve, were in Surrey to the south of London, and consisted of a corps comprised of the 1st Armoured Division and two or three infantry divisions (including the 1st Canadian), plus an independent tank brigade, and separately, the nearly complete 2nd Armoured Division.

The British Army was more or less fully motorized, albeit than some units were short of transport, and there were only about 400 tanks available, roughly half of them Matilda heavy infantry vehicles.

The backbone of the defense of Britain was, however, not the army, nor even the Royal Air Force, but the Royal Navy.  There were about 90 destroyers in home waters by early September, of which 70 were within a few hour’s steaming of the invasion beaches, plus about three dozen cruisers, several battleships and battle cruisers, a couple of aircraft carriers, and many smaller warships.  Supported by motor torpedo craft, and during daylight hours by Fighter Command, destroyer flotillas led by light cruisers were expect to wreck havoc among the invasion convoys.  The battleships, aircraft carriers, and their supporting warships were to remain out of the range of enemy aircraft until opportunity presented itself to intervene against German convoys.

The Game.  Play began on game date Sept. 8, 1940, which allowed the players to take some actions based on incoming intelligence.  The German decided to implement the landings along the southeastern and southern coast of England on the night of the 21st-22nd,  The plan called for six separate landing sites, from Ramsgate, at the north end of the English Channel, to Lyme Regis, in the southwest, a front exceeding 200 miles without considering the convolutions of the coast.

What happened next can be briefly summarized, albeit at the expense of some interesting detail.

During the predawn darkness on Sept. 22nd, German mine fields and light naval forces prevented the Royal Navy from intervening forcefully against the first wave invasion convoys, though the Germans did take some losses.  Elements of nine German divisions managed to get ashore at several points along the coast, and an airborne division captured an airfield in Kent.  During the day, major air battles erupted all over southern England.  Meanwhile, British ground troops began to move into action, as the Germans overran beach defenses and began moving inland, capturing the port of Newhaven in Sussex.

There was considerable naval action overnight on the 22nd-23rd.  A German diversionary attack from Norway was dispersed with heavy loses by the Royal Navy.  Meanwhile, the Royal Navy committed seventeen cruisers, nearly 60 destroyers, and strong light forces to sweeping the English Channel, suffering some casualties, but inflicting heavy losses on the German Navy and shipping.  By dawn on the 23rd the Germans had lost about a quarter of their invasion fleet, between hostile fire and the hazards of the sea, with heavy casualties among the troops.

On the 23rd, the German ground troops began a drive on Folkestone, hoping to capture the port.  Meanwhile, the RAF heavily punished ships and landing barges on the beaches, and struck at embarkation ports in France and Belgium.  In the course of the day, the German 22nd Airlanding Division captured the airfield at Lympne, in Kent, though British artillery and commando attacks prevented them from making use of it.  The British began counterattacks, blocking a drive on Hastings in Sussex, while Newhaven was recaptured with the help of the Australians.  An attempt by the New Zealanders to block the German drive on Folkestone was defeated when they were attacked in the rear by the 22nd Airlanding Division, and the port fell into German hands.

During the 23rd both sides committed their air forces to support the ground forces, while the RAF also continued attacks on German bases across the Channel, with heavy loses all around.

Although the Germans had elements of 10 divisions ashore, perhaps 90,000 men, most units were still awaiting their second echelons.  These could not be dispatched across the Channel due to the presence of the Royal Navy and deteriorating weather.  Late in the day the senior German players held an acrimonious staff meeting, during which the Army demanded reinforcements, while the Navy pointed to the poor situation in the Channel, and the Air Force protested a shortage of resources, since it was still bombing London and other cities while also trying to cover the invasion.  A decision by the senior German player (“Hitler”) resulted in orders for second wave forces at Calais to cross to Folkestone, leaving troops further west along the coast in Sussex to fight it out with diminishing supplies.

Overnight on the 23rd-24th, the Germans advanced on Canterbury and Dover in Kent, but they were less successful in Sussex.  Meanwhile, the Calais-Folkestone convoy managed to get to sea before dawn, as the weather cleared.  But about daylight a British destroyer flotilla found the convoy about ten miles out to sea, and cut it to pieces, despite escorting U-boats and motor torpedo boats.  The Luftwaffe intervened, but the RAF threw in 19 fighter squadrons.  While the British suffered serious damage to several cruisers and destroyers, nearly two-thirds of the German transport barges were sunk. Though some small ships managed to make it to Folkestone, the port was so seriously damaged they could only unload slowly.

This air-sea fight in the Channel was the decisive action of the campaign.  German forces ashore in England were rapidly running out of men, equipment, and ammunition, and were unable to effect further advances; at best they might be able to hold out for a week or so on what was at hand.  With perhaps three-quarters of the German transport barges lost, further reinforcement was unlikely.  As British ground forces began pressing the invaders back into their bridgeheads, the Germans ordered an evacuation.  By enormous effort, the Germans were able to pull out about 15,400 of the 90,000 troops who had landed in England.  Final casualties, British and German, were not calculated, though losses during sea actions and air operations had been heavy.

Critique.  Following the game the participants took part in a general analysis.  Some interesting observations and conclusions were made.  The British GHQ mobile reserve had not been engaged at all.  In addition, casualties to the Royal Navy had been serious, but hardly devastating; of about 90 destroyers on hand, only five had been sunk and six seriously damaged, and only three of the three dozen cruisers had been lost, and three more heavily damaged.

All participants, German as well as British, agreed that the outcome was an accurate assessment of the probable result of an actual invasion.

Oddly, the Sandhurst wargame was designed on the basis of inaccurate information.  Some time after the game, additional hitherto secret documents came to light, which revealed that the Germans probably had even less chance of success than they did in game.  At the time the game was designed, the true extent of British “stay behind” forces, intended to conduct guerrilla operations in the rear of the invasion forces, and the sheer scale of defensive installations that had been erected across southern England in anticipation of an invasion were still classified; there were some 28,000 pill boxes, coastal batteries, strong points, blockhouses, anti-aircraft sites, and some other installations.

So assuming Hitler had for a time been serious about invading England, his decision to call it off was probably wise.

"These things must be done delicately-- or you hurt the spell."  - The Wicked Witch of the West.
"We've got the torpedo damage temporarily shored up, the fires out and soon will have the ship back on an even keel. But I would suggest, sir, that if you have to take any more torpedoes, you take 'em on the starboard side."   Pops Healy, DCA USS Lexington.


bayonetbrant

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Reply #1 on: July 17, 2019, 08:36:38 AM
sounds like an early Megagame

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BanzaiCat

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Reply #2 on: July 17, 2019, 12:44:54 PM
Great read, thanks for posting.  :bigthumb:

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Silent Disapproval Robot

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Reply #3 on: July 19, 2019, 09:38:19 PM
Would the loss of all those destroyers have been enough to change the outcome of the U-boat war?  Brits lost 452,000 tonnes of shipping while the bulk of the RN destroyers were tied up in channel defence.  After the threat of invasion passed and the destroyers were released for escort duty, tonnage sunk dropped to 156,000 in late 1940.



besilarius

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Reply #4 on: July 24, 2019, 07:05:33 AM
That is a very good question.
Offhand, my feeling is that there was a real shortage of escorts without this invasion.  At this time convoys often had thirty merchant vessels escorted by very few anti submarine craft.  I think as few as four was common.  The extra losses from the channel fighting would have made this situation worse.
However, so much depended on the Uboat finding the convoy.  They did not have radar, relying totally on visual.  The visual horizon from a Uboat was quite small, I think about eight miles.
There was direction from Donitz's headquarters from land based direction finding, and the very successful codebreaking team.  There just weren't that many Uboats to stop al the convoys.
The merchant losses would have been greater, but not that much more, I think.

"These things must be done delicately-- or you hurt the spell."  - The Wicked Witch of the West.
"We've got the torpedo damage temporarily shored up, the fires out and soon will have the ship back on an even keel. But I would suggest, sir, that if you have to take any more torpedoes, you take 'em on the starboard side."   Pops Healy, DCA USS Lexington.


bayonetbrant

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Reply #5 on: July 25, 2019, 09:05:07 AM
I don't know that there's any way the Germans would've been able to successfully invade the UK.  I've played around with a variety of games purporting to play it out, and ultimately, the Germans just have an unsustainable logistics problem.

But...

could the Germans have legitimately starved out the UK and brought about their surrender, if they cut back on the shenanigans in North Africa and instead focus their national-level logistics efforts on building more ships/u-boats to more effectively blockade the UK?  Or does that just hasten US involvement?

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BanzaiCat

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Reply #6 on: July 25, 2019, 10:04:41 AM
They could have continued their North Africa shenanigans and not invaded Russia. Focusing on the naval and air war at that point, plus dominating the Med and invading Gibraltar/Malta would have gone a long way to dominating the UK. Fortunately for the future, it didn't work out that way.

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JasonPratt

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Reply #7 on: July 25, 2019, 02:17:15 PM
They had to do the North Africa shennanigans, for almost the same reason they had to invade Russia: because Germany didn't have major sources of rare minerals necessary to construct things like submarines and airplanes, and their only allied source for oil worth mentioning was Romania. Which was about to be steamrolled by Stalin. Who had been providing the lion's share of rare minerals and oil to Hitler up to this point anyway.

Hitler was well aware that sooner or later Stalin would stop supplying Germany with the materials necessary to wage war, and at that point Germany, who had made themselves the enemy of the world, would be doomed. He had no choice but to try to secure a line of communication to sufficient alternate supplies, or else just give up and shoot himself (sooner rather than later ;) ). Italy tried to provide that supply through their own North African reconquista of the previous Roman Empire, but it soon became clear that they weren't up to the job: they could sort-of secure the sea lanes (sort of, thought not very well, as long as Britain had naval and air bases in the Med), but they couldn't punch through to the resources. Not with Britain in the way.

On top of those factors, Hitler can see that Stalin is gearing up to come after him -- even though he can't quite see just how much Stalin is gearing up. (The logistic transferral of the Soviet Second Strategic Echelon which started 3rd quarter 1940, has to be regarded as the premier logistic achievement and counter-intelligence coup combined in world history. With Hitler's spoof of Stalin's estimations on the German invasion timetable running a close second on counter-intel.)

Once those factors are taken into account (not even counting what Hitler doesn't and can't know yet about how hard Stalin is preparing to invade), the only way for Hitler to win Sealion is to successfully bluff Sealion instead of actually doing it. If he can convince Britain to sue for peace, then he has some chance of surviving and holding part of Europe -- if he can also punch the Soviet Union so hard and so fast that it sparks a revolution overthrowing Stalin, leaving Hitler's national socialism as the dominant legacy of Marx.

That's a lot of ifs, all of which were also dependent on Hitler not being Hitler and his Nazis not being Nazis. Which, unfortunately for him, duh. ;) Going after Poland was his biggest and most fatal mistake, in the long run; as well as "being the Nazis". Without the latter, Germany could have expected help from the Allies to deal with Stalin, on par with the help Stalin was receiving to prepare to deal with Hitler.