I would use 1911a1 too, back then. If they let me I'd take my Model 19 no dash, for a bug, I'd carry it too. Wear the Model 19 in an across the chest holster and the 1911a1 in a flap, but for sure the 1911a1 would stay in my hand most of the time, if I was down in a tunnel.
My current weapons are the same things I'd use in WWII, Korea, or Viet Nam, except in Korea and WWII the Combat Magnum would have been a N-Frame, or maybe even something small like a Police Positive, or j-frame like a Model, 60 in the Viet Nam era, or nowadays a 642.
My Grandfather was an Army Ranger 1st Lieutenant in WW2. I'm pretty sure all he had was a knife and 1911a1 for his up close and back up weapons. He even had a hand made knife, because at the time he went to the Pacific Theater, K-Bars and things like that were scarce. He had a double edged dagger, that was made by Naval Armorers. It was the same one they made for Navy Raiders and Combat Demolition Units.
The weapons that were available during Vietnam Conflict, are still viable. My .308 M1 and Rem 700 still work. However, they'd work better combined into one, in the form of an AR10 with optics. Right now in 2012, instead of a 1911a1 my Glock 19, or 20 with light mounted would be better, especially for going into a confined space, looking for enemy combatants.