(a) Wills offered for probate, except nuncupative wills, must be proved by one or more of the subscribing witnesses, or if they be dead, insane or out of the state or have become incompetent since the attestation, then by the proof of the handwriting of the testator, and that of at least one of the witnesses to the will. Where no contest is filed, the testimony of only one attesting witness is sufficient.
(b) If none of the subscribing witnesses to such will are produced, their insanity, death, subsequent incompetency or absence from the state must be satisfactorily shown before proof of the handwriting of the testator, or any of the subscribing witnesses, can be received; in addition to the methods already provided, the will of a person serving in the armed forces of the United States, executed while such person is in the actual service of the United States, or the will of a seaman, executed while such seaman was at sea, shall be admitted to probate when either or all of the subscribing witnesses is out of the state at the time said will is offered for probate, or when the places of address of such witness or witnesses are unknown upon the oath of at least three credible witnesses, that the signature to said will is in the handwriting of the person whose will it purports to be. Such will so proven shall be effective to devise real property as well as to bequeath personal property of all kinds.