at any military, air, or naval base acquired after January 1, 1940, by the United States from any foreign government; or

upon any lands occupied or used by the United States for military or naval purposes in any Territory or possession outside the continental United States (including the United States Naval Operating Base, Guantanamo Bay, Cuba; and the Canal Zone); or

upon any public work in any Territory or possession outside the continental United States (including the United States Naval Operating Base, Guantanamo Bay, Cuba; and the Canal Zone), if such employee is engaged in employment at such place under the contract of a contractor (or any subcontractor or subordinate subcontractor with respect to the contract of such contractor) with the United States; but nothing in this paragraph shall be construed to apply to any employee of such a contractor or subcontractor who is engaged exclusively in furnishing materials or supplies under his contract;

under a contract entered into with the United States or any executive department, independent establishment, or agency thereof (including any corporate instrumentality of the United States), or any subcontract, or subordinate contract with respect to such contract, where such contract is to be performed outside the continental United States and at places not within the areas described in subparagraphs (1)–(3) of this subdivision, for the purpose of engaging in public work, and every such contract shall contain provisions requiring that the contractor (and subcontractor or subordinate contractor with respect to such contract) (1) shall, before commencing performance of such contract, provide for securing to or on behalf of employees engaged in such public work under such contract the payment of compensation and other benefits under the provisions of this chapter, and (2) shall maintain in full force and effect during the term of such contract, subcontract, or subordinate contract, or while employees are engaged in work performed thereunder, the said security for the payment of such compensation and benefits, but nothing in this paragraph shall be construed to apply to any employee of such contractor or subcontractor who is engaged exclusively in furnishing materials or supplies under his contract;