Once the second war had begun what forces were sure to be a formidable foe

The RAF (Britain Royal Air Force)

Explanation:

This period was where battle was fought in the air. It was a battle between the British Royal Air Force and the Luftwaffe (Nazi German Air Force) in 1940. The plane pilots of both the Raf and the Luftwaffe took to the air to battle each other out with their war plane in battle for the control of the air space in Germany, English Channel and Britain.

But in contract, the Luftwaffe force who fort gallantly met their match with the Raf who indicate to be a formidable enemy.