text: Tactical Mission Tasks
  REDUCE
  B-54. Reduce is a tactical mission task in which a unit destroys an encircled or bypassed enemy force.
  This task can occur at any location on the battlefield. Reduce is also a mobility task to create and mark lanes
  through, over, or around an obstacle to allow the attacking force to accomplish its mission (ATP 3-
  90.4/MCTP 3-34A). There is no symbol for this task.
  RETAIN
  B-55. Retain is a tactical mission task in which a unit prevents
  enemy occupation or use of terrain. A commander assigning this task
  specifies the area to retain and the duration of the retention, which is
  time or event driven. While a unit is conducting this task, it expects
  enemy forces to attack and prepares for decisive engagement. A unit
  tasked to retain a specific piece of terrain does not necessarily have to
  occupy it. The direction of the arrow has no significance, but the symbol
  includes the entire area to be retained. Figure B-24 depicts the retain
  tactical mission task.
  Figure B-24. Retain task
  SECURE
  B-56. Secure is a tactical mission task in which a unit prevents the
  enemy from damaging or destroying a force, facility, or
  geographical location. This task normally involves conducting area
  security operations. A force given the mission of securing a unit, facility,
  or geographic location, such as a route or base, not only prevents enemy
  forces from over running or occupying the secured location, but also
  prevents enemy direct fires and observed indirect fires from impacting
  the secured location, unit, or facility. Stated simply, the secured area or
  location is safe enough to build and project combat power. There is a
  difference between control and secure. The control tactical mission task
  Figure B-25. Secure task
  allows enemy direct and indirect fires to affect the location being
  controlled while secure does not. A unit does not have to physically occupy the area immediately around the
  unit, facility, or geographic location it is securing if it can prevent the enemy from occupying or firing at that
  location by other means. The commander states the mission duration in terms of time or event when assigning
  a mission to secure a given unit, facility, or geographic location. The direction of the arrow has no
  significance, but the symbol includes the entire area to be secured. Figure B-25 depicts the secure tactical
  mission task.
  SEIZE
  B-57. Seize is a tactical mission task in which a unit takes possession
  of a designated area by using overwhelming force. An enemy force
  can no longer place direct fire on a seized objective. The arrow points to
  the location or objective to seize. This task differs from secure because
  it requires offensive action to obtain control of the designated area or
  objective. It differs from the task of occupy because it involves
  overcoming anticipated enemy opposition. Once a friendly force seizes
  a physical objective, it clears the terrain within that objective by killing,
  capturing, or forcing the withdrawal of all enemy forces. Figure B-26
  depicts the seize tactical mission task. Figure B-26. Seize task