Explanation:

About Sahayak system in the Indian Army:
•    While officers of the army during colonial rule were supposed to have a retinue of servants — an official list from the late 19th century mentions 39 such servants — they needed help when in battle. Thus evolved the concept of ‘batman’, short for ‘Battle Man’, wherein a young soldier helped out an officer with some of his mundane activities.
•    The practice has since been codified via an Army Order and other policy letters into the Sahayak system.
•    Sahayaks are authorised to Officers and Junior Commissioned Officers when serving with units or Headquarters functioning on War Establishment, i.e., those units which mobilise for war.
•    The Indian Air Force and the Indian Navy do not have a system of Sahayaks for officers.
•    However , It is supposed to be a voluntary job, and any soldier expressing a desire to not be a Sahayak is supposed to be excused.