In 1898, a series of revenue stamps featured the battleship Maine, tragically sunk in the Havana harbor just a few months before, a mysterious event soon followed by the Spanish-American War. War with Spain brought with it a need to pay for the expense of military action — a need for new revenue, and new revenue stamps.
To fulfill the immediate need, U.S. postage stamps were overprinted with the initials “I.R.” for Internal Revenue (Scott R153-R158B). Newspaper stamps were similarly overprinted for use as provisional revenues (R159-R160).