Bradleys Head Fortification Complex, Military fortification in Sydney Harbour National Park, Australia.

Bradleys Head Fortification Complex is a military installation in Sydney Harbour National Park featuring gun emplacements, tunnels, and ammunition storage positioned to defend the harbour's strategic entrance. Walking paths and interpretive signs guide visitors through the various structures and explain how they functioned together as a defensive system.

Convict labour began a gun pit and sandstone firing wall at Bradleys Head in August 1840, after Captain George Barney proposed defences and two American warships entered the harbour unannounced in November 1839. The battery was the only one completed by 1850 and fell out of use in 1859. From 1870 James Barnet supervised three new gun pits, a riflemen's gallery and interconnecting tunnels, with the first guns in place by 1871.

The site is also known as the HMAS Sydney 1 Mast and Associated Memorials, and the ship's mast stands here as a naval memorial. The complex lies just south of Taronga Park Zoo, within Sydney Harbour National Park at Mosman, and is now a war memorial and recreational area.

The grounds are open year-round and offer good views of the harbour and city skyline from various vantage points. Paths connect the main features, though some areas are steeper and walking shoes with proper grip are helpful.

The 1871 barracks and its three gun pits were cut directly from the sandstone of the headland rather than built up from imported stone, so parts of the fort are the rock itself. The complex also carries the mast of HMAS Sydney I, a memorial element added long after the guns fell silent in 1859.