That whenever in conformity with the laws of this state, an enrollment of all persons subject to military duty shall be ordered and made, it shall be the duty of all officials and persons charged with the making of such enrollment to separately enroll and designate in all such counties or districts as the commander-in-chief shall designate, all persons liable for military duty under the laws of this state who shall be included in any of the following classifications, that is to say:

   First, All seafaring men of whatever calling or occupation;

   Second, All persons engaged in navigation of the lakes, rivers or other waters of this state;

   Third, All persons engaged in the construction or management of ships or crafts (or any part thereof) upon such waters;

   Fourth, All ship owners and their employes;

   Fifth, All yacht owners;

   Sixth, All members of yacht clubs and other organizations formed for the pursuit of aquatic sports and pastimes; and

   Seventh, All ex-officers and former enlisted men of the United States navy, which said separate enrollment and designation shall be made and returned in like manner as provided by law for the enrollment and return of the names of persons liable for military duty under the laws of this state: Provided, however, That all persons included within the fourth and sixth classifications above given and not included within any of the others of said classifications may, if they shall so elect, be included in the general enrollment of persons liable for military duty in theland forces of the militia, instead of in a separate enrollment and designation provided for by the terms of this act.