((a)) For the purposes of the laws administered by the Secretary, the Secretary, and those employees to whom the Secretary may delegate such authority, to the extent of the authority so delegated, shall have the power to—
((1)) issue subpoenas for and compel the attendance of witnesses within a radius of 100 miles from the place of hearing;
((2)) require the production of books, papers, documents, and other evidence;
((3)) take affidavits and administer oaths and affirmations;
((4)) aid claimants in the preparation and presentation of claims; and
((5)) make investigations and examine witnesses upon any matter within the jurisdiction of the Department.
((b)) Any person required by such subpoena to attend as a witness shall be allowed and paid the same fees and mileage as are paid witnesses in the district courts of the United States.