The Maritime Administrator is prepared to provide facultative war risk insurance policies covering any cargoes described in § 308.501 which are designated by an applicant prior to the attachment of risks, if the applicant does not have an Open Cargo Policy issued by the Maritime Administrator, or if he has a shipment which is not covered by his Open Cargo Policy. However, a person with regular shipments is urged to avail himself of the advantages of the automatic coverage of an Open Cargo Policy. The Maritime Administrator reserves the right to decline to quote rates or bind insurance on shipments of cargo that could be covered by an Open Cargo Policy unless the applicant can show to the satisfaction of the Maritime Administrator that the risk is not one of a series of similar risks forming part of a continual flow of business for the applicant. The policy will be in the standard form of War Risk Facultative Cargo Policy, Form MA-316, prescribed in § 308.545. All policies shall be issued by Underwriting Agents appointed by the Maritime Administrator. All Underwriting Agents shall be domestic insurance companies authorized to do a marine insurance business in a State of the United States.