Vessels subject to the provisions of this part are:

(a) All vessels which may in the future be constructed or sold with construction-differential subsidy allowances and/or national defense features allowance under Title V or VII of the Merchant Marine Act 1936, as amended.

(b) All vessels which have previously been constructed or sold with construction-differential subsidy allowances and national defense features allowances under Title V or VII of the Merchant Marine Act, 1936, as amended;

(c) All vessels which have previously been constructed with construction-differential subsidy allowances or national defense features allowance under Title V or VII of the Merchant Marine Act of 1936, as amended, and later adjusted in price pursuant to section 9 of the Merchant Ship Sales Act of 1946;

(d) All vessels which are subsidized under operating-differential subsidy agreements.