Definition of At priority call

DOD Dictionary of Military Terms
at priority call
(*) A precedence applied to the task of an artillery unit to provide fire to a formation/unit on a guaranteed basis. Normally observer, communications, and liaison are not provided. An artillery unit in “direct support” or “in support” may simultaneously be placed “at priority call” to another unit or agency for a particular task and/or for a specific period of time.
  

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