Sentence:  On a cloudy day one can hop in and out of the clouds, greatly to the annoyance of some <WSD>Archie</WSD> commander who, just when he has got range and direction and is about to let fly, finds that his bird has disappeared into a cloud. He fills thatcloud with HE but his quarry emerges from another nearby with a gesture of derision which the gunners below may imagine, though cannot see. On a sunny day, <WSD>Archie</WSD> is up early, for he knows that aircraft will be silhouetted against a blue sky. Then the experienced pilot hops in and out of the sun, there being no clouds, while the <WSD>Archie</WSD> commander rubs his smarting eyes and uses strong words. 
Meaning of the word marked with <WSD> tags:  Anti-aircraft artillery.