Conversation so far:
Did Arthur Tedder, 1st Baron Tedder have a military office in the war?
Arthur Tedder was promoted to lieutenant in the Dorset Regiment. He was posted to a reserve unit at Wyke Regis on the Dorset coast where he seriously injured his knee.

Question: How did he hurt his knee?
Self-contained rewrite: How did Arthur Tedder, 1st Baron Tedder hurt his knee?