What is "subsistence department"

Subsistence Department \Sub*sist"ence De*part"ment\ (Mil.) A staff department of the United States army charged, under the supervision of the Chief of Staff, with the purchasing and issuing to the army of such supplies as make up the ration. It also supplies, for authorized sales, certain articles of food and other minor stores. It is commanded by any officer of the rank of brigadier general, called commissary general, and the department is popularly called the Commissary Department.