When a unit with the Infiltrate keyword starts its Activaiton, if it is undeployed, it may Deploy by placing the unit leader of that unit completely within allied Territory. Then the remaining miniatures in that unit are placed in Cohesion with their unit leader and completely within allied Territory. Miniatures cannot overlap impassable terrain when they are placed using Infiltrate.Many actions, such as Infiltrate, allows you to deploy without spending an action. The infiltrating unit will have 2 remaining Actions after its deployment.[Source] 