Section 4M. There shall be within the executive office for administration and finance a department of veterans' services under the supervision and control of a commissioner of veterans' services, who shall be appointed by the secretary of administration and finance, with the approval of the governor, and who shall serve at the pleasure of the secretary and may be removed by the secretary at any time subject to the approval of the governor. This position shall be classified in accordance with section forty-five of chapter thirty and the salary shall be determined in accordance with section forty-six C of said chapter thirty. The commissioner shall devote his full time during business hours to the duties of his office. He shall be the state agent for the settlement of pension, bounty, back pay, compensation and other claims of citizens of the commonwealth against the government of the United States, or any state thereof, on account of military or naval service, and he shall assist and advise war veterans, and their dependents, heirs or legal representatives, with respect to the filing, prosecution and settlement of such claims.