In order for military service to be considered to be creditable under the Railroad Retirement Act, it must have been performed during one of the following periods:

(a) April 21, 1898, through August 13, 1898—Spanish American War;

(b) February 4, 1899, through April 27, 1902—Philippine Insurrection;

(c) May 9, 1916, through February 5, 1917—Mexican Border Disturbances;

(d) April 6, 1917, through November 11, 1918—World War I;

(e) September 8, 1939, through June 14, 1948—National Emergency and World War II. Individuals required to continue in service after this period may be credited with the service if:

(1) They were in military service on December 31, 1946, or

(2) They were required to remain in military service involuntarily after December 31, 1946;

(f) June 15, 1948, through December 15, 1950. This service is creditable if:

(1) Entered into involuntarily; or

(2) Entered into voluntarily, but only if:

(i) The individual who seeks credit for this service performs service as an employee for an employer as defined in part 202 of this chapter either in the year of his or her release from active military service or in the year following such release, and;

(ii) The individual does not engage in any employment not covered by part 203 between his or her release from active military service and his or her commencement of service for an employer.

(g) December 16, 1950, through September 14, 1978—National Emergency.