Signal Hill Battery, Coastal artillery battery in Watsons Bay, New South Wales, Australia.

Signal Hill Battery is a fortified coastal defense installation in Watsons Bay featuring exposed gun positions and subterranean military structures. The site overlooks Sydney Harbour's entrance and displays the characteristic layout of such harbor-protection facilities from the late 19th century.

The installation was constructed in 1892 and equipped with a British Armstrong 9.2-inch disappearing gun designed for harbor defense. The gun remained in active service until its final firing in 1933.

Two plaques placed on 30 March 1993 set the reserve in its historical context, and a memorial was installed in November 1992 by the Royal Australian Signal Corps Association on behalf of its members. The gun pit itself is a visible reminder of the Armstrong disappearing-gun design, in which the barrel retracted below the parapet after firing.

The battery stands beside the Signal Hill Lighthouse on Old South Head Road in Watsons Bay. The underground complex beneath the road is sealed: its street entrance has been tack welded shut, so it cannot be entered. The gun barrel is not on site; it is displayed at North Fort on North Head, at the northern end of the Memorial Walk.

Beneath the surface lies a sealed network of corridors, ammunition storage rooms, and other chambers that once served the gun crews. This hidden infrastructure reveals how sophisticated the site's engineering was despite its modest above-ground appearance.