The British had been hugely successful at breaking German codes in the First World War. The Germans were determined not to let that happen again. This time they had Enigma, a code machine that produced messages that could not be decrypted. Or so the Germans believed.
The navy Germany had at the outbreak of the Second World War was only a small fraction of what the Allies had arrayed against it. But the Fall of France and the entry of Italy into the war changed things dramatically and created opportunities at sea that Germany had never had in the last war.
In 1940, the British government was in the frustrating position of funding research on a number of promising projects that would be valuable to the war effort, but with the Battle of Britain in full swing, British factories had to turn out fighter planes as fast as they could. There was no room for development of experimental new technologies, so the British turned to the United States
Italy's invasion of Greece was disastrous. With the British also advancing in North Africa, and a surprise air attack disabling three Italian battleships, it was no longer possible to pretend that Italy was a equal of Germany.
Benito Mussolini wanted to prove that Italy was an equal partner with Germany in the Axis alliance, so he began a war with Greece.
Germany found that it could not defeat the British on their home island; the UK was unable to fight the Germans in Europe. So what next?
When France collapsed, Roosevelt redoubled his effort to aid Britain. But there was also a Presidential election to think about; Roosevelt won an unprecedented third term.
America was preoccupied with domestic issues during the run-up to the war. When the war came, the Roosevelt Administration looked for ways to aid the Allies despite the limitations of the Neutrality Act.
More on various genres of pulp fiction, and how they led to the development of comic books.