(a) The Secretary is authorized to provide by regulations for waiving the payment of premiums on United States Government life insurance on the due date thereof and the insurance may be deemed not to lapse in the cases of the following persons:
(1) those who are confined in hospital under the Department for a compensable disability during the period while they are so confined;
(2) those who are rated as temporarily totally disabled by reason of any injury or disease entitling them to compensation during the period of such total disability and while they are so rated;
(3) those who, while mentally incompetent and for whom no legal guardian had been or has been appointed, allowed or may allow their insurance to lapse during the period for which they have been or hereafter may be rated mentally incompetent, or until a guardian has notified the Department of the guardians qualification, but not later than six months after appointment of a guardian. In mentally incompetent cases the waiver is to be made without application and retroactive when necessary. Relief from payment of premiums on the due date thereof shall be for full calendar months, beginning with the month in which said confinement to hospital, the temporary total disability rating, or the mental incompetency began or begins and ending with that month during the half or major fraction of which such persons are no longer entitled to waiver as provided above.