Sarah Paine

So this is Hitler's happy time when he's sinking an awful lot of stuff.

Then there's a big Greenland gap.

This is where there's a lack of air cover.

And so you'll see a lot of things are going down in this Greenland gap.

But meanwhile, the British have gotten pretty good at espionage and they've captured a lot of Enigma machines.

Those are what the Germans are using to encrypt their messages.

Well, the British capture some machines, some rotors, some code books in 1940 and 41.

So by the summer of 1941,

through February 42, they can actually read the codes or some of them, decrypt them, so that within 36 hours, they can get the information out.

And this allows convoys to go, oh, Wolfpack there, we're going to do evasive routing of the convoys somewhere else.

And that may have saved up to 2 million tons of Allied shipping.

But meanwhile...

For the Germans, General Rommel is in North Africa, and he's having troubles because he's supplied across the Mediterranean, and the British and friends are sinking too many of his supplies.

So Admiral Dunitz is told to reroute some of the U-boats in the Atlantic to go help General Rommel up in North Africa.

The United States isn't in the war, so all quiet on the

on the eastern seaboard.

So it's looking like it might be okay for the British for a while, except Donitz thinks something's up.

And so they add a fourth rotor to the Enigma machine.

And so the British are then blind again for most of 1942 until they can capture a four-rotor Enigma machine, all the rotors plus the code books.

It takes a while.