If author Peter Fleming's commas were thorns, if his footnotes were barbed wire, and if his frequent obscure foreign phrases and literary allusions were broken glass, many a reader of "Operation Sea Lion" would be bleeding to death after the first twenty pages and retreating for good. (See other amazon reviews.)
Somehow, Fleming needed three or four chapters to warm up before making his main thesis clear. It is that:
(1) German plans in 1940 to invade Britain after the fall of France were uncharacteristically sloppy and uncoordinated.
(2) Only Admiral Raeder, the head of the German navy, realized the incredible complexity of a huge cross-channel operation, and Germany's inability to carry it off with the limited resources he commanded. Raeder never quite told the Fuehrer.
(3) Hitler, himself the chief proponent of invasion planning, vacillated repeatedly between believing in an outright invasion, on the one hand, or expecting Britain's impending political capitulation, on the other.
(4) Germany's attacks on RAF installations and aircraft factories had Britain on the ropes by September of 1940, but, out of pique at the RAF's bombing of Berlin, it threw the Luftwaffe instead against metropolitain London, where they were more vulnerable to ground and air attacks and imposed far less military damage to the British war machine.
(5) By 1941, the invasion was a chimera. The Luftwaffe was weakened, and Hitler's head had been turned by the prospect of taking the Soviet Union.
Fleming takes far too long to get his story out. He wastes a lot of time describing (poorly and incompletely) British efforts to defend itself against invasion, and tells the German view of the story in a jumbled chronology, sometimes leading the reader to wonder what in the world was going on. Just in time, though, his choppy writing style finally improves (though he's still far to enamoured of footnotes for my taste).
Before you buy this one, I'd do some more research, in amazon or elsewhere. The topic's important and instructive enough to warrant your time. It's dead certain that later books on Sea Lion had better access to archives and eyewitness than did Fleming, and will tell the tale more coherently.