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Wargaming Sea Lion

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besilarius:
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.

JasonPratt:
EPIC! -- I didn't know the sides had gamed things out shortly after the war!  :D :notworthy:

While Hitler had been wise not to press an invasion of England without dealing with the RAF first or the RN (practically impossible), he had other problems gaining steam in the east. Stalin was waiting for Sealion at first, as an opportunity to invade. The Germans didn't find out until well into Barbarossa just how much preparations Stalin had been making (the arrival of the vaunted "Black Corps" of the 2nd Strategic Echelon shutting down Hitler's advance for a while, was a terrible surprise -- and had started moving westward around November 1940, in the largest successful logistic operation in human history so far), but Hitler was well aware that Stalin wanted to invade and had been making major offensive preparations. So the ongoing risk of having an axe sunk in his back, especially against his Romanian oil reserves, kept Hitler from being unwilling to commit fully to invading England.

Ultimately, Hitler used Sealion itself as a "maskirovka" for spoofing Stalin about Hitler's plans to stop-hit invade Russia, while both sides built up blitzkrieg oriented forces on their now-common borders. (Stalin had been invading neutral nations meanwhile, and even had a border now directly on East Prussia.) Whoever managed to strike first would catch the other side completely out of effective defensive position, but while Stalin had the advantage of plenty of land to sacrifice for time (and a second strategic echelon already on the move to his western border, with a 3rd and 4th already in planning, not even counting around two million elite-trained troops in reserve being trained as air-mobile units, which he started doling out as whole armies starting in 1943 or late 42), Hitler had the advantage of combat-experienced troops who weren't cripplingly overspecialized for blitzkrieging Central and Western Europe (ironically): Hitler's forces could fight better on Russian territory against armored opponents than Stalin's forces could (at the time)!

One major part of Hitler's masquerade in the final moves before Barbarossa, involved keeping up the pretense of his invasion staff headquarters still being camped out in northern France. Stalin already knew from his spies that Hitler had given up on Sealion, but Hitler successfully spoofed him on this point: from Stalin's perspective, he thought Hitler was keeping his supergenerals ready to go on defense against an allied opportunity strike to gain a port foothold in Western Europe, and missed them being secretly shuffled over to Germany's East Front. (There were some other things Stalin was watching for, too, which Hitler intentionally or accidentally spoofed him on, due to Hitler's plan against the USSR not being what Stalin expected.)

Tripoli:

--- Quote from: JasonPratt on July 17, 2019, 07:47:15 AM ---EPIC! -- I didn't know the sides had gamed things out shortly after the war!  :D :notworthy:



--- End quote ---

I believe the book "Operation Sealion" by Richard Cox was written about this wargame.  This is going back to the very dim recesses of my memory.....

Hot lead and dirty talk!:
Cool story, thank you for posting this

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