I joined the TA in 1938 when I was 17. My mother, a widow had to give written permission. She was not at all enthusiastic.
I joined the Royal Engineers by mistake. My friends joined the Royal Artillery. I didn't hear the distinction between RE and RA, and the reason - When I was 10 years old I had mastoid and totally lost the hearing in my left ear. So I was half deaf.
To my surprise I had to pass a medical. MO check OK. Eyesight 20/20. Hearing - "very good" despite 50% loss of hearing.
I stood in a queue for about 20 minutes, debating if I should just go home and forget about the TA. But the disgrace....
It dawned on me that the sergeant checking hearing was following a set pattern. Standing behind the recruit he brought an army watch in from behind the right ear and said "Let me know when you hear the tick" He followed that up with "Good, now the other ear" He always started with the right ear (my only hearing ear) After he said "good" to this ear, I calculated that I could count 4 slowly, before he said good to the left ear. When it became my turn I used my formula, got a couple of goods and was in.
That was 1938. I was demobilised in 1946, and no one ever found out.