The change from Chamberlain to Churchill was not a sure thing.
Many Brits did not trust Churchill -- too eratic, too, well, imaginative.
And now Norway is added to Galipoli in his list of "accomplishments." Oh dear.
So Chamberlain's first choice as successor was his Foreign Secretary, Lord Halifax. But for reasons an American might never understand, that was impossible.
The selection then fell reluctantly to Churchill.
Among Churchill's many assets was an ever deepening friendship with Franklin Roosevelt. In the end, this would make all the difference.
Whether he knew it then or not, Chamberlain was, or would soon be, mortally ill with bowel cancer and die almost six months to the day later, age 71.
So, do I have to pay a penalty for jumping the gun? ;-)
As an American, I still consider Churchill a better leader than Roosevelt. Roosevelt was a socialist who cozied up too close to Uncle Joe. Churchill recognized the evil regime of both Hitler and Stalin before many would listen.