a. Any member of the National Guard who has reached the age of sixty-four years, or shall be retired from service under applicable laws and regulations of the United States, shall be transferred to the state retired list by order of the Governor.

b. Any officer who has served for at least twenty years in the National Guard, or in the National Guard and the Armed Forces of the United States combined, upon his request, may be transferred to the state retired list in a grade one grade higher than the highest grade previously held by him during such service. In computing such twenty-year period, service as an enlisted man shall be counted.

c. Any enlisted man who has served at least twenty years in the National Guard, or in the National Guard and the Armed Forces of the United States combined, upon his request may be transferred to the state retired list by the Governor in a grade equivalent to the highest grade held by him during such service. If said grade was of officer grade, the provisions of subsection b of this section will govern.

d. Any officer of the National Guard may be transferred to the state retired list on his own request, approved by the Adjutant General.

e. Any officer of the National Guard who has been rendered surplus by reduction, disbandment, or reorganization of a unit or for any other reason, unless transferred to the inactive National Guard, may be relieved from duty and command and may be transferred to the state retired or reserve list.

f. Any person who has served as an officer in the National Guard or in the Armed Forces of the United States and has been honorably discharged therefrom, may be commissioned and placed on the state retired list in the highest grade previously held by him after complying with such conditions as may be prescribed by regulations issued pursuant to this chapter.