Postal officials in the field are subject to full military discipline under the Army Act. Superior officers wear field service khaki uniform with badges of rank and the letters "Post" in brass on the shoulders. A Deputy Postmaster-General or Assistant Director-General of the Post Office ranks as a Lieutenant-Colonel, and a Superintendent as Major, Captain or Lieutenant, according to his grade and length of service. Subordinate officials, if Europeans, are classed as Assistant Commissaries, Sub-Conductors or Sergeants, according to their pay, and Indians are given rank as Subadars, Jemadars, Havildars or Naiks. Field allowances, in addition to pay, are fixed according to a sanctioned scale, the rate for a Director or Superintendent being 25 per cent of his pay, subject to a minimum monthly allowance of Rs.100 in the case of the latter. Inspectors and Postmasters draw Rs.90 a month in addition to pay, other subordinates being remunerated at a lower rate. In virtue of the military rank held by them, officers and subordinates are entitled to all privileges and advantages for service in the field, such as wound pensions, family pensions, medals and compensation for loss of baggage. The officer in charge of field post offices is attached to the head-quarters of an Expeditionary Force as adviser to the Military Authorities on all postal matters; he is required to visit the base and field post offices as frequently as possible, and is responsible for the proper working and efficiency of mail arrangements. He arranges with headquarters for carriage of mails between the base and the field, fixes the hours of despatch of mails from all post offices and the hours during which money orders are issued, and also settles the question of making over cash collections to the nearest Field Paymaster, Treasure Chest Officer, Regimental Accounts Officer or Post Commandant, as the case may be. The development of the Field Postal System has been gradual and has undergone many changes. The earliest record of a regular Indian Post Office staff proceeding for active service with a military force is in connection with the Persian Expedition of 1856. The establishment consisted of two clerks, an interpreter (moonshee) and four peons, and, as no suitable departmental officer could be found to take charge of the arrangements, the Government of Bombay appointed the Military Paymaster of the Persian Expeditionary Force to take control.