(a)"active duty", in relation to a person subject to this Act, means any duty as a member of the Force during the period in which such person is attached to, or forms part of, a unit of the Force–(i)which is engaged in operations against any enemy, or(ii)which is operating at a picket or engaged on patrol or other guard duty along the borders of India, and includes duty by such person during any period declared by the Central Government by order as a period of active duty with reference to any area in which any person or class of persons subject to this Act may be serving;