What is the military term used for attacking an enemy when they are least prepared?

The military term for attacking an enemy when they are least prepared is "Surprise." In military strategy, achieving surprise is crucial because it can exploit the enemy's vulnerabilities, disrupt their plans, and gain a tactical advantage. Surprise attacks can lead to a more favorable outcome with reduced risk to the attacking forces, as the enemy may not have sufficient time to react or counter the offensive. This term encapsulates the element of timing and the advantage derived from unpredictability, which is fundamental in achieving operational success on the battlefield.

While "Ambush" relates closely to surprise, as it typically involves unexpectedly engaging an enemy, it has a more specific connotation, often implying that the attacker lies in wait for the opponent. "Strike" generally refers to the act of attacking but does not specifically denote the element of surprise. "Engagement" is a broader term that denotes contact with the enemy and does not specifically address the element of attacking when the enemy is least prepared. The most fitting term that embodies the concept of seizing the opportunity for an attack when an enemy is vulnerable is "Surprise."