Which form of maneuver is used when an attacking force attempts to move undetected into an area occupied by enemy forces?

Infiltration is the correct response because it specifically refers to the tactic where an attacking force seeks to penetrate an area containing enemy forces without being detected. The primary goal is to achieve surprise and engage the enemy from within their positions, allowing for targeted attacks or the disruption of enemy operations while minimizing exposure to direct confrontation.

This maneuver is characterized by a stealthy approach, leveraging terrain, timing, and tactical elements to bypass enemy defenses rather than confronting them head-on. It allows forces to exploit gaps in the enemy's security and to create confusion or disorganization.

The other tactics involve more direct confrontations or broader strategic maneuvers. A frontal assault involves attacking the enemy head-on, which is the opposite of attempting to move undetected. Encirclement involves surrounding the enemy to cut off their movement or supplies, and envelopment entails attacking the enemy's flanks to encircle them, both of which require more pronounced movement into enemy territory rather than careful infiltration.