Which tactical mission task involves sudden and surprise action against an enemy?

The tactical mission task that involves sudden and surprise action against an enemy is the ambush. An ambush is specifically designed to catch the enemy off guard, often using concealment and careful planning to initiate an attack at a moment when the enemy is least expecting it. This tactic allows the attacking force to achieve a decisive advantage, inflicting damage or disruption before the enemy has a chance to respond effectively.

In contrast, reconnaissance attacks are primarily focused on gathering intelligence about enemy positions and movements rather than delivering a surprise attack. Defense involves preparing to repel an enemy assault rather than initiating surprise action against them. Countermeasures typically refer to actions taken to counteract hostile actions, such as deploying counter-batteries or electronic warfare, and don't inherently involve surprise attacks. Thus, an ambush is the correct answer, as it epitomizes the concept of attacking the enemy unexpectedly and decisively.