An election made to adopt and use the LIFO inventory method is irrevocable, and the method once adopted shall be used in all subsequent taxable years, unless the use of another method is required by the Commissioner, or authorized by him pursuant to a written application therefor filed as provided in paragraph (e) of Sec. 1.446-1. [T.D. 6500, 25 FR 11730, Nov. 26, 1960]