What tactical task involves replacing all or part of a unit in an area?

The tactical task that involves replacing all or part of a unit in an area is known as "relief in place." This operation is typically conducted in situations where a unit is rotated out of a combat position or area of operations, allowing another unit to take over its responsibilities and maintain the continuity of operations.

During a relief in place, careful coordination and planning are essential to minimize risk and ensure that the outgoing unit can effectively transition responsibilities to the incoming unit. This task often includes detailed briefings, the sharing of intelligence, and the systematic transfer of control of the area to ensure that no gaps in coverage occur and that operational integrity is maintained throughout the transition.

Other options, while related to movement and tactical operations, do not specifically refer to the direct replacement of forces in a given area. For instance, linkup is focused on two friendly units coming together in a designated area, passage of lines refers to one unit crossing through the positions of another for continued operations, and patrol involves conducting reconnaissance or security missions, which do not entail the replacement of one unit by another.