§ 80. Tenure of commissioned officers. No commissioned officer shall be involuntarily discharged or dismissed from the service, unless by the senate on the recommendation of the governor, stating the grounds for such recommendation; or by the sentence of a court-martial; or upon the findings of an examining board appointed pursuant to section seventy-five of this chapter; or, as provided by section seventy-eight of this chapter, for absence without leave for a period of three months; provided, however, that a commissioned officer may be transferred to the state reserve list or state retired list as provided by section twenty and section twenty-one of this chapter, respectively.