I hate to pull a "KEITH" on you guys but I know or have worked with some of these actors you have mentioned and I have to let you know that in the majority of cases the persona they portray on screen is far far different than who they actually are in real life.
Lee Marvin was similar to the characters he played on screen and I'm proud to say he spent time in the Corps when the serving was extra tough.
There were many top Hollywood actors, producers, directors, etc., who served time under actual combat conditions during WWII and some who even flew many missions over German occupied battlefields without getting their asses shot off.
But in the majority of cases, what you see on screen is not what you get in real life settings.