Operating in a tactical environment requires thorough observation of the area around a group's position. A technique used to ensure 360 degree security during a movement, a halt, or to ensure coverage of the area around a defensive position is the assignment of sectors of fire for all individuals and fighting positions. A Sector of Fire is an assigned area which is required to be covered by the fire of an individual or a crew served weapon system. Sectors of fire are assigned during all phases of an operation to include both offensive and defensive missions. Assigning sectors of fire allows individuals to prioritize where they are to scan, helping them focus their efforts creating better surveillance and better use of resources. Individuals should only engage threats that enter their sector of fire. A benefit of assigning sectors of fire during the defense is that all group members do not fire upon a single target revealing all of their positions. A key to defensive operations is to not disclose your position's location until absolutely necessary. You often hear a technique used by an opposing force called "Probing" which allows the enemy to test a defensive position in order to document position locations in order to find weaknesses. If a group does not assign individual sectors of fire they risk the possibility that more than one position initiates fire on a single threat creating a breach of security when all positions fire at once. When establishing a defensive position leaders allocate sectors of fire for each individual by identifying a "Left Limit" and "Right Limit" of fire for each position. Left and right limits are imaginary lines from the individual's firing position to a designated identifiable point on the ground. Leaders should always use terrain features and manmade structures to designate left and right limits. Once the position's left and right limits are identified the individual must document the azimuth and the distance to each limit's object/point along the limit line. A copy of the positions is sector of fire is provided to the group leadership so the individual sectors of fire can be combined in to a group sector sketch. The group sector sketch is used to confirm all area to the front of the defensive position is covered by direct fire and the positions provide mutual support to each other. Leaders must conduct a briefback rehearsal to ensure clear individual understanding of their assigned sectors of fire. The designation of individual sectors of fire significantly increases a group's survivability during an attack.