Abstract: A tamperproof fire hydrant which can only be operated with the use of a special operating tool thus preventing the opening of the hydrant by unauthorized persons for unauthorized use. Additionally the tubular hold-down nut for the operating nut is so designed to prevent unauthorized disassembly of the hydrant by unauthorized personnel. To prevent unauthorized use or unauthorized disassembly the polygonal shaped operating nut is concealed by a dome shaped cap covering both the hold-down nut and the operating nut, the cap being freely rotatable with respect thereto. The dome shaped cap permits only limited access to the operating nut. Additionally the hold-down nut for the operating nut is also protected in this manner and is provided with a specifically shaped outer surface which requires a special tool usable only when the dome shaped cap for the operating nut is removed.