During the '40s and World War II, cigarettes were freely given the 'boys' in uniform - many by the Red Cross and volunteers at departing trains. And in mess kits probably, as Joe said. Dad was in England and asked Mom to send him cigarettes - perhaps the demand over there was greater than the supply? She was limited to, I believe, three cartons a month - allowing for a pack-a-day smoker but no extras to use for trade - a common commodity along with candy and gum and just about anything in short supply.
Let's not forget the influence of the movies - they made smoking manly for men and chic for women - probably the biggest influence of all on the public. Smoking was near universal back then.