This subchapter is designed to supplement systems of mortgage insurance under other provisions of this chapter in order to assist in providing adequate housing in areas which the President, pursuant to section
1591 of title
42, shall have determined to be critical defense housing areas. The Secretary is authorized, upon application by the mortgagee, to insure under this section or section
1750g of this title as hereinafter provided any mortgage which is eligible for insurance as hereinafter provided and upon such terms as the Secretary may prescribe to make commitments for the insuring of such mortgages prior to the date of their execution or disbursement thereon: Provided, That the property covered by the mortgage is in an area which the President, pursuant to section
1591 of title
42, shall have determined to be a critical defense housing area, and that the total number of dwelling units in properties covered by mortgages insured under this subchapter in any such area does not exceed the number authorized by the Secretary of Housing and Urban Development from time to time as needed in such area for defense purposes and to be insured pursuant to this subchapter: Provided further, That in the event the Secretary has issued a commitment to insure a mortgage under this section, which commitment was in force and effect on June 1, 1953, and the Secretary determines that, because of changes in defense requirements, there is reasonable doubt that such housing is needed for defense purposes and that it is probable that the mortgage would become immediately in default and claim made for payment under the mortgage insurance contract if the unit or units are completed and the mortgage insured, the Secretary is authorized, in the interest of conserving the General Insurance Fund, to pay (in cash from the General Insurance Fund) to the mortgagee for the account of the mortgagor such amount as the Secretary shall determine to be necessary to reimburse the mortgagor the amounts paid or to be paid by the mortgagor on account of labor performed and materials in place, less the Secretary’s estimate of the reasonable salvage value of such materials, plus an allowance for development costs equal to 4 per centum of the principal amount of the mortgage specified in such commitment, and no payments shall be made pursuant to this proviso unless a claim therefor is filed not later than six months from date of the determination of lack of need and the claim is in such form and contains such supporting information, documents, and data as the Secretary may require: Provided further, That the aggregate amount of principal obligations of all mortgages insured under this subchapter shall not exceed such sum as may be authorized by the President from time to time for the purposes of this subchapter pursuant to his authority under section
1715h of this title: Provided further, That the Secretary shall have power to require properties covered by mortgages insured under this subchapter to be held for rental for such periods of time and at such rentals or other charges as he may prescribe; and, with respect to such properties being held for rental,