The topic of why vintage jackets are so short comes up often and the typical excuse is the rise of the pants worn at the time. I did a little looking into it and the average height of US males in 1940 was 5'7". So from what I can tell the jackets are short by today's standard because the average height was some 2-3" shorter than the average height today. It's not pants...it's evolution.
From what I recall it was more specifically Depression era malnutrition for the short 40s/50s heights.