Either I missed something but in the first episodes it seems that the soldiers training for the Airborne were more or less volunteers who didn't have any real war experience. The TV show then shows them training and the next thing they are dropped over Normandy in perhaps one of the most sophisticated military missions to date. Is this portrayal accurate? I imagined that the US airborne divisions primary consisted of battle-hardened infantry men, which had received Airborne training only after they had proven themselves in the battlefield..
The US Airborne program began in June 1940 with a test platoon, although the concept dated back to the First World War. Following the German paratrooper operation on Crete in 1941 (which was really disastrous, but the US didn't know that), the US began heavily stepping up the Airborne program. To gain ones jump wings, you had to complete the very rigorous training, culminating with five successful jumps. There would eventually be 5 full divisions, the 82nd, 101st, 11th, 13th, and 17th, plus half a dozen other Parachute Infantry Regiments, sometimes attached to divisions.
The 82nd was the first initiated, and the first to see action as a division in their drop in Sicily. The 509th was first to make a jump in North Africa. The 101st, of which Band of Brothers depicts were first put into action for the Normandy invasion. The men were volunteers, as paratroopers received an extra $50 pay a month. As the miniseries shows, the men trained together for roughly two years before being sent to England for the invasion.
But outside of a handful who may have been transferred into the unit from other PIRs, the bulk of the 101st were completely battle-free. As were virtually all American soldiers, sailors, and Marines when we entered the war. There were some who had previously served in World War I, but these were very few that would be in a low rank to train for active combat. Some few other may have served in the Marines in the Banana Wars (see Chesty Puller), but essentially every Division put into action anywhere was green its first time, which included the Airborne. And really, how could it have been otherwise? There would be no realistic way to take only combat-veterans, THEN train them to become paratroopers for months or years, and get them back into action. It was difficult enough maintaining numbers in units already in action, much less deplete their numbers of experienced veterans and replace them with untested men. The necessities of war prevent such action. We needed men when we needed them, and not later. The 13th Airborne, for example, was activated in 1943, but didn't complete training and arrive in Europe until February 1945. They were the only Airborne division sent to Europe that never saw combat.
The Airborne training proved substantial, however. Despite being their first taste of war, the 101st proved themselves very well in Normandy (unlike some other divisions) and went on to win laurels in Holland, and especially at Bastogne in late 44.