I always thought (inevitably) that the Secret Weapon was Radar ... and the C&R system ...
... we have two secret weapons, Radar and C&R and indominatble courage ...
... we have three secret weapons, and we are BRITISH!
... and Free French, and Polish, and Czech, and Aussie, and Kiwi, and Canuck ...
Who do you think you are, Mister Hitler ... ?