Winston Churchill became Prime Minister of Great Britain at the age of 65 on this date in 1940. May 10, 1940 was a moment of dynamism militarily and politically as Hitler’s forces swept across Belgium en route to France. One purported bulwark—the famed Maginot Line—quickly became a relic, while one supposed relic—Mr. Churchill—began his finest hour.
Writing about that time now 70 years ago, Richard Nixon said:

The Second World War gave Churchill a backdrop commensurate with his larger than life abilities and personality. It seems a sad fact of life that great leadership seems most evident only under the terrible conditions of war.

Churchill himself later recorded his thoughts about that moment in May of 1940 as part of his voluminous memoir of World War II:

Thus, then, on the night of the tenth of May, at the outset of this mighty battle, I acquired the chief power in the State, which henceforth I wielded in ever-growing measure for five years and three months of world war, at the end of which time, all our enemies having surrendered unconditionally or being about to do so, I was immediately dismissed by the British electorate from all further conduct of their affairs.

During these last crowded days of the political crisis, my pulse had not quickened at any moment. I took it all as it came. But I cannot conceal from the reader of this truthful account that as I went to bed at about 3 a.m., I was conscious of a profound sense of relief. At last I had the authority to give directions over the whole scene. I felt as if I were walking with Destiny, and that all my past life had been but a preparation for this hour and for this trial. Eleven years in the political wilderness had freed me from ordinary party antagonisms. My warnings over the last six years had been so numerous, so detailed, and were now so terribly vindicated, that no one could gainsay me. I could not be reproached either for making the war or for want of preparation for it. I thought I knew a good deal about it all, and I was sure I should not fail. Therefore, although impatient for the morning, I slept soundly and had no need for cheering dreams. Facts are better than dreams. — Winston Churchill, The Gathering Storm