Of course they can.
TRUE
Yes
Yes
right
true
false
"Anything's fair in love and war"
Attacked is the action verb in the sentence, "The enemy attacked the headquarters."
The role of paratroopers (Airborne Troops) was to create a 3rd dimension in warfare, and a 3rd Front (Front, Flank, and Rear). The paratroopers were dropped BEHIND enemy lines. The fortunes of war may have allowed some men to land on enemy lines, and/or the enemy lines were fluid (mobile) and they moved to that position, or US/Allied intelligence missed those positions, and didn't plan for them (didn't know they were there).
When the enemy gets a nuke
No, shooting descending enemy paratroopers is a violation of the laws of war and the rules of engagement. It is important to adhere to international humanitarian law and treat all individuals, even enemy combatants, with dignity and respect.
Because they were landing at night in unexplored enemy held territory.