1. Officers of the Customs in the Island of Puerto Rico, ceded to the United States by Spain, may issue a certificate of protection, entitling a vessel to which it is issued to the protection and flag of the United States on the high seas and in all ports, if the vessel is owned by:
a. A citizen of the United States residing in Puerto Rico.
b. A native inhabitant of Puerto Rico upon taking oath of allegiance to the United States.
c. Resident of Puerto Rico before April 11, 1899, hitherto a subject of Spain, upon abjuring his allegiance to the crown of Spain and taking the oath of allegiance to the United States.
2. The master and the watch officers of a vessel to which a certificate of protection is issued shall be citizens of the United States or shall take the oath of allegiance to the United States, providing that the general commanding the forces of the United States in Puerto Rico may in his discretion in special cases waive these requirements in whole or in part.
3. Such certificate of protection shall entitle vessel to the same privileges and subject it to the same disabilities as are prescribed in Article XX of the Consular Regulations of 1896 for American or foreign built vessels transferred abroad to citizens of the United States.
4. The form and manner of the issue of certificates of protection provided for in this order shall be prescribed by the Secretary of War.
William McKinley, Executive Order Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/205352