Berlin, Germany · September 17, 1940

In November 1939, some two months after Germany had invaded Poland, Grand Admiral Erich Raeder, head of the Kriegs­marine, in­structed a subordi­nate to draw up a paper on “the pos­si­bility of troop landings in Eng­land.” The study paper set out four pre­requi­sites. The next month the Wehr­macht (Ger­man armed forces) issued its own paper, also laying out four pre­requi­sites. Following Ger­many’s swift occu­pa­tion of France and the Low Coun­tries in May and June 1940, and Adolf Hitler’s growing impa­tience with British indif­fer­ence toward his recent peace feelers, the Ger­man leader for­mally set in motion pre­para­tions for Opera­tion Sea Lion (See­loewe), the cross-Channel inva­sion of Eng­land. Sadly for Ger­many, the fail­ure of Hermann Goering’s Luft­waffe in August–Septem­ber 1940 to defeat the Royal Air Force, despite in­flicting punishing losses, con­vinced the Kriegs­marine’s high com­mand that the in­va­sion was too risky. Not being certain of the approaching win­ter weather, Hitler wisely de­cid­ed on this date in 1940 to post­pone the in­va­sion until a new date could be set. The Luft­waffe still had orders to con­tinue its attacks on Brit­ain. Instead of air­fields and other mili­tary instal­la­tions, the Luft­waffe now tar­geted indus­trial cen­ters and, finally, on Septem­ber 7, 1940, the city of London. This phase of the air war over Britain was called the Blitz (Septem­ber 7, 1940, to May 10, 1941), and was Hitler’s way of pun­ishing the Brit­ish for refusing to sur­render. Assisting the Luft­waffe in pun­ishing Eng­lish cities was a small con­tin­gent of Ital­ian fighters and bombers, the Ital­ian Air Corps (Corpo Aereo Itali­ano, or CAI), which over a 100-day period had little to show for its effort, earning the mocking nick­name “The Chianti Raiders” whenever RAF pilots acted to inter­cept the Ital­ian enemy. The Battle of Brit­ain (July–October 1940)—the air war that was Opera­tion Sea Lion’s pre­landing phase—cost the Luft­waffe 1,733 planes against 915 British fighters and took all the wind out of Sea Lion’s sails. Hitler’s am­bitions for domi­nating Europe now turned toward the Soviet Union, which was in a 10‑year non-aggres­sion pact (Molotov-Ribben­trop Pact) with an incor­rigible aggres­sor. Opera­tion Barba­rossa, launched June 22, 1941, proved a fatal mis­take. In just short of four years the capi­tal of Hitler’s Thou­sand-Year Reich, menaced on every side by Soviet armies and shrunk to a few hun­dred square yards, became the Nazi leader’s tomb on April 30, 1945.

The Battle of Britain Halts Operation Sea Lion, the 1940 German Invasion of England

Barges being readied for Operation Sea Lion, Wilhelmshaven, August 1940German Pionierlandungsboot 39, Soviet Union, 1941

Left: Lacking purpose-built landing craft, the Kriegs­marine impro­vised with in­land freight barges in the lead-up to Opera­tion Sea Lion, as shown here at Wilhelms­haven, August 1940. Approxi­mately 2,400 were col­lected from all over Nazi Europe (half from the Nether­lands). Of these only about 800 were powered (some poorly); the rest had to be towed by tugs. Converting the assembled river barges into landing craft for troops, tanks, and vehicles was compli­cated. Some barges could accom­mo­date three or four tanks. After Sea Lion was can­celled, the Kriegs­marine used some of the moto­rized barges for landing on Soviet-held Baltic islands but most were returned to their former service.

Right: In the late 1930s the Kriegsmarine ordered the develop­ment of pur­pose-built landing craft, which were tested in the Baltic Sea begin­ning in March 1941. Not until Septem­ber 1941, a year after Sea Lion was can­celled, was the first in a series of landing craft, the Pionier­landungs­boot 39 shown here, avail­able. Excepting the last in the series, the landing craft were assembled from two mir­rored pieces, which could be trans­ported by rail to the coast or river entry. The Pionier­landungs­boot 39 was nearly 50 ft long and 15 ft wide and cap­able of carrying 20 tons. This landing craft was first used during Opera­tion Bar­ba­rossa, Hitler’s inva­sion of the Soviet Union. The largest and last in the series, Pionier­landungs­boot 43, was 116 ft long, 28 ft wide, and could carry 95 tons of cargo.

He 111s over Britain, 1940London docks and warehouses burning, September 7, 1940

Left: German bombers (He 111s) over Britain. From the per­spec­tive of Ger­many, the fifteen weeks of aerial com­bat known as the Battle of Brit­ain (July–October 1940) was an attempt to whittle away at the Royal Air Force, there­by giving the Luft­waffe air supe­ri­ority during Opera­tion Sea Lion. Stymied by the RAF on the one side and by their own lack of com­bined opera­tional com­mand on the other, the Ger­mans switched from bombing mili­tary com­plexes to bombing cen­ters of indus­try and popu­lation, inadver­tently per­mitting the RAF to regroup and replace its lost aircraft and installations.

Right: The first heavy bombing of London’s docks came on the night of Septem­ber 7, 1940 (“Black Satur­day”), the start date for the London Blitz. The huge pall of smoke bil­lowing from river­side ware­houses and docks could be seen for miles. Fires raged right up to Tower Bridge. Like the Battle of Brit­ain, the Blitz never achieved its in­tended goals of either demor­al­izing Brit­ish poli­tical and mili­tary leaders into capit­u­la­tion or signi­fi­cantly damaging the coun­try’s eco­nomy to con­tinue the war. (Over its nine months, the Blitz killed more than 43,000 civil­ians.) By the time the last bombs had fallen on Lon­don on May 10, 1941, in a par­tic­u­larly murderous cli­max to the Blitz, the inva­sion threat had passed, and Hitler’s atten­tion was directed eastwards to the Soviet Union.

Alternate History: Operation Sea Lion, the Successful German Invasion and Occupation of England