Generally speaking, a night raid did not mean slipping in late at night and quietly killing enemies in their sleep. Instead, the attackers used some means to startle most of the sleeping enemy awake and throw them into confusion. With preparations already in place, better-organized formations, and weapons and armor at the ready, the attackers could then launch a one-sided massacre of their panicking foes.
This was not a tactic that could be used at will. First, the attacking soldiers had to be elite troops capable of seeing at night. Otherwise, their tightly assembled army would scatter before the battle even began.
Second, they had to be seasoned veterans who would not let the surrounding chaos affect their composure. They needed to calmly kill disorganized enemies running wildly in every direction without breaking ranks themselves.
Third, they needed sufficient intelligence and a basic understanding of the enemy camp.
The Dwarves met all these requirements. By the time Allen returned to the Dwarven camp from Thranduil's camp, evening was already approaching.
Once Balin and Dáin learned that the Elves had agreed to their proposed plan, they began preparing the Dwarven warriors in camp for battle. Since this was to be a surprise attack, they made little commotion. The Dwarves kept a constant watch on the Easterling camps, but were the Easterlings not watching theirs just as closely?
Any unusual activity in the Dwarven camp now would be tantamount to telling the Easterlings, I'm coming for you. Get ready.
To avoid alerting the Easterlings to their plan beforehand, Balin and Dáin ultimately decided to take only three hundred of their finest Dwarven veterans. Each received a black cloak to cover any plate armor that might gleam in the moonlight. After all, of the three races, Dwarves were the weakest at short bursts