Late in the evening of August 17, 1886, Troop M, First United States Cavalry, marched into Yellowstone National Park, relieved the Park Superintendent of his duties, and inaugurated a new era of national park administration. When Yellowstone was established in 1872, the park was administered by civilian appointees who had neither physical or legal means to stop the vandalism, poaching, and trespassing that threatened its existence. Some Congressmen, faced with this apparent failure, labeled the park concept an absurdity. Congress declined to appropriate money for the continued operation of the Yellowstone, and the Secretary of the Interior was forced to request troops to protect the park in 1886. The resulting military management eventually extended to the Yosemite, General Grant, and Sequoia National Parks.  The period of military administration of the national parks is unique in American history. Before 1894 in the Yellowstone, and throughout its administrative career in the California parks, the cavalry operated without a legal framework or means of law enforcement, but over thirty-two years of military guardianship, a national park policy and administrative practices evolved. Moreover, when the National Park Service began operating in 1918, it took over from the military an already trained cadre of rangers. In a very real sense, the cavalry laid the foundations of the National Park Service and saved the parks for the more than 307 million people who now visit our national parks each year.