How large a proportion of British and American troops were involved in direct combat with the enemy in World War II? What was the casualty rate among those men?
I believe the "Tooth-to-tail ratio", the ratio of combat personnel to support personnel, is a useful guide for how many troops would have been involved in fighting. This is a slightly dodger proposition today in wars without a front-line (where logistics personal have a very real prospect of being engaged), but seems reasonable for WW2. I happen to be concentrating on American figures rather than British.
The Other End of the Spear: The Tooth-to-Tail Ratio (T3R) in Modern Military Operations by John J. McGrath provides some of the information we need on this. For example it seems that while US command aimed for 65% combat troops, they attained about 40% in the European theatre. Later on, US forces in Korea has almost the same TtT ratio so this seems generally applicable. I will be assuming the theatre TfT ratio this is very close to the Army TfT ratio, but given the size of the army compared to other services this seems reasonable.
Here are Wikiepdia's causalities figures of course. But, the Congress Research Service have some that differentiate by service, so I'll be using these and looking only at the army. There were about 235,000 "battle deaths" and 83,400 other deaths out of about 11.2 million soldiers. Death rate here of 2.8%. Assuming our 40% combat troops ratio applies to the army generally, that gives us about 4.5 million combat personnel. Which results in about a 6% death rate if we attribute all battle deaths and a proportional share of the "other" deaths to these combat personnel.
All these numbers are a bit less than triple that if we include non mortal wounding as well (ie casualties rather than deaths). And I will say I've made more assumptions here than I am happy with, so don't get too excited about these numbers.
But note that it varies from source to source , and maybe a book could give better information's.
One way to estimate an answer is to first count up all the "hard fighting" (i.e. famous) U.S. Army and Air Corps units.
Just the Army Air Corps units in Europe and the Pacific include about 500,000 men who participated in air operations (with about 70,000 casualties).
Now add in the U.S. Marines. That adds in another 200,000 who were in serious combat.
Then add in the twenty infantry, airborne, and armored divisions that did about 90% of the fighting in both theaters. Including casualties, that is easily another 500,000 men who actually participated in deadly combat.
The U.S. Navy? Not a high percentage of casualties, but when you consider that the fleet off of Okinawa carried at least a quarter million sailors and all of them would have been exposed to hundtrds of kamikazes, then include Iwo Jima, Leyte invasion, Pearl Harbor, the prolofic naval combats in the Solomons and across the Bismark arch, then thats gotta be another million men who actually went in harm's way.
Then ballance that number against the millions of men who were trained but arrived i theater after the fighting was over.
I estimate that about 25% of U.S. military actually participated in deadly combat. Probably an equal number experienced light combat. For example, my dad was in the Merchant Marine and watched Jap bombers hit a Liberty ship about three miles away, but in four years his ship was never targeted; also, while sailing in the Gulf of Alaska, his ship came upom a life boat full of (frozen) dead men who had been on a Liberty Ship that was torpedoed by a Jap sub (? ??Probably? No one really knows).
My dad never considered himself a "combat veteran" however.