War changes a lot of peacetime habits. Training, for example, suddenly becomes a lot more realistic, and effective. That's because there's now a way to tell which training works, and which doesn't. Training suddenly becomes very focused, addressing battlefield needs, and preparing troops for what they will actually encounter. This phenomenon has been the case in the American armed forces for over two centuries.
The reality shock delivered by a war always shakes up the standard training procedures. In peacetime, training tends to develop, unofficially, but very decisively, goals that have little to do with combat needs. In peacetime, pet theories, political considerations, and budget problems all exert influence. Professional soldiers try to resist a lot of this, but always lose some ground in the readiness (for combat) department. It's another reason for the old saying about troops, "it's not a matter of who's better, but who's worse."
There are still many people around who remember the training reforms that took place during World War II, Korea and Vietnam. In an unusual, and fortuitous development, the reforms did not end when the U.S. pulled out of Vietnam, which was unusual. The changes kept coming, resulting in the 1980s NTC (National Training Center), and many other innovations. But as was discovered in 2003, some things were missed. For example, there was a trend towards less live fire practice with small arms. Because of political pressure, and timidity by senior army generals, basic training for non-combat troops was fatally diluted.
Even while the Iraqi invasion was going on, it was clear that the combat training was inadequate for combat support troops. For the combat troops, there was a need to develop new tactics, or brush up on old ones, for dealing with ambushes and irregular warfare. This quickly led to innovations like "Road Warriors University" in Kuwait (where non-combat troops could practice firing their weapons from moving vehicles, among other useful practices.) Computer based simulations were quickly adapted to the unique needs of combat in Iraq and Afghanistan.
As happened as far back as World War II, there was also the establishment of a feedback system, to get the trainers the latest information on what tactics and techniques the enemy was using. The Internet makes this a lot easier, as during World War II much of the work was manual, with company commanders getting crudely printed (mimeographed) handouts once or twice a month, containing tips on what new techniques the enemy was using, and how to counter them. These crib sheets were also flown back to the United States, where trainers modified their drills and exercises. Today, the exchange of information it not only quicker, but interactive and often immediate. Chat rooms and video conferencing enable platoon sergeants, in the combat zone, to let drill sergeants, at the training centers, know exactly what new techniques need to be taught.
As great captains have noted for centuries, "speed in battle is essential" for victory. Speed in training is equally essential, and keeps down friendly casualties.