On the grounds of Arlington National Cemetery.
The mast of the U.S.S. Maine was removed from the ship in 1905 shortly before the ship was taken out to sea and sunk with military honors. The mast was then installed above a memorial in Arlington National Cemetery in honor of those who lost their lives when the ship sank in Havana, Cuba, Harbor in 1898. This sinking was the event that started off the Spanish-American War.
Thumbnail from Google Earth.