Influenced by Alfred Thayer Mahan, Roosevelt called for a build-up in the country's naval strength, particularly the construction of battleships.[94] Roosevelt also began pressing his national security views regarding the Pacific and the Caribbean on McKinley, and was particularly adamant that Spain be ejected from Cuba.[95] He explained his priorities to one of the Navy's planners in late 1897:

I would regard war with Spain from two viewpoints: first, the advisability on the grounds both of humanity and self-interest of interfering on behalf of the Cubans, and of taking one more step toward the complete freeing of America from European dominion; second, the benefit done our people by giving them something to think of which is not material gain, and especially the benefit done our military forces by trying both the Navy and Army in actual practice.[96]
On February 15, 1898, USS Maine, an armored cruiser, exploded in the harbor of Havana, Cuba, killing hundreds of crew members. While Roosevelt and many other Americans blamed Spain for the explosion, McKinley sought a diplomatic solution.[97] Without approval from Long or McKinley, Roosevelt sent out orders to several naval vessels, directing them to prepare for war.