Stage 4 - Vietnam - Hot LZ
The helicopter replaced the horse and that reinvigorated cavalry tactics.
Cavalry during the Civil and Indian wars (and before) would navigate rapidly to the flanks, or even behind the enemy, dismount and form a skirmish line. Cavalry is frequently the "tip of the spear" during an assault, or the last to leave the battlefield during a retreat. The helicopter brought these cavalry tactics back into spotlight, even more so due to the very challenging terrain of the Vietnamese battlefields.
During the Vietnam conflict, forces were dropped straight into the fight - frequently exiting the helicopter while under direct fire, this being referred to as a Hot LZ.
We're going to get a lot of comments on this, but the Colt SP1's A1 birdcage IS period correct, although maybe not specifically for the Battle of Ia Drang. The original 3 prong flash hiders were prone to damage, collection of debris, and abuse by the soldiers so the A1 birdcage replaced them gradually over time, starting as early as 1967.