2300 men and 18 cannon totally surprised the Trenton garrison during the traditional hangover following traditional Christmas celebrations.
BTW, neither James Flexner in his definitive biolgraphy of Washington, nor McCullough in his recent book "1776," believed the Hessians were hungover. They were shocked by the attack and by Rall's death during the opening stages of the battle.
Rall havd information from the MSM that an attack might occur, but the timing in a driving snow and by its ferocity was overwhelming. His pickets were awake and fired several vollies but were driven in quickly. Rall was rallying his troops as they quickly mustered, but was stopped short. All in all, we were, as Washington always acknowledged, aided greatly by "Providence."
Tyson