text: FM 7-100.1 ________________________________________________________________________________
  PERSONNEL SUPPORT
  12-69. Units may maintain strength by piecemeal replacement of casualties
  during combat, particularly when lightly wounded personnel and damaged
  equipment can return to parent units quickly. Once casualties are sufficient
  to threaten total loss of combat effectiveness, the unit withdraws from
  contact and reconstitutes. Timely replacement of ineffective units is vital to
  maintaining momentum. The commander may choose to withdraw heavily
  attritted units and consolidate them to form a smaller number of combat-
  effective units.
  12-70. The OSC chief of administration is responsible for all personnel
  actions and transactions in the command. The personnel support battalion
  provides the personnel to operate the personnel operations center. That
  center’s major functions include providing personnel and administrative
  support, finance support, and legal support.
  REPLACEMENT
  12-71. Replacement operations are based on unit strength reports and
  include the coordinated support and delivery of replacements and soldiers
  returning from medical facilities. The unit strength report is used to assess a
  unit’s combat power, plan for future operations, and assign replacements on
  the battlefield.
  Individual Replacements
  12-72. The OPFOR can use the system of individual replacements in both
  peacetime and wartime. The sources of replacement personnel are school
  graduates, reserve assignments, medical returnees, and normal assignments.
  Incremental Replacements
  12-73. The OPFOR may incrementally replace entire small units such as
  weapons crews, squads, and platoons. Replacements can be obtained from
  training units or reserve forces.
  Composite Unit Formations
  12-74. Composite units may be formed from other units reduced by combat
  operations. Composite units may be constituted up to OSC level.
  Whole-Unit Replacement
  12-75. The OPFOR uses whole-unit replacement when massive losses occur
  as a result of a combat action. Company-level and above units are brought
  forward from reserve forces to replace combat forces rendered ineffective.
  Replacement Training
  12-76. OPFOR planners realize that personnel replacement requirements
  may necessitate any of the aforementioned procedures. Individual and unit
  replacement exercises are held semiannually to maintain established
  proficiency standards for personnel units. During these and other training
  exercises, troops are moved by various modes of transportation such as motor
  vehicles, waterway, aircraft, or rail.