Everyone, everywhere was smaller in the world before WWII, and even for quite a while after in many places. We are all getting taller, and bigger around, and working less hard in the developed world. My Dad was in the Navy in WWII, and we have his dress blues. They fit me when I was 14, and there is no way my 17 year old could get into them, which is the age Dad was when the uniform was made for him. There are lots of factors, but food availability/nutrition certainly was part of it.