The Middle Ground Coastal Battery is an islet off the coast of Mumbai (Bombay), India. The isle, situated a few dozen metres away from the Gateway of India, lies in the Thane Creek. The islet is actually a piece of hard basalt rock, emerging from the creek bed, having an area of a few hundred square metres.

The Middle Ground Coastal Battery was once part of a reef, like the nearby Oyster Rock . After the setting up of the British East India Company in Bombay, the island was fortified in 1682 to curb the sea piracy in the area. Later a marine police force comprising of Bhandaris were stationed there to keep an eye on the pirates who used to board the ship. The Bhandaris were chosen for their loyalty, honesty and local knowledge. With their yellow turbans and blue trousers, the police were a formidable sight. After piracy moved to the South China Sea, about two hundred years ago, the police were disbanded and the Royal Navy gained control of the rock.

The British added to the fortifications with the use of cannons and later on three anti-aircraft guns to protect the harbour from a perceived Japanese invasion during World War II. The guns are replaced by more modern anti-aircraft guns, but the deep cylindrical mountings of the old guns still remain.

The island is manned by a staff of three sailors of the Indian Navy who keep in touch with the mainland through a wireless set. Currently the island serves as the saluting base to the commanding-in-chief of the Western Naval Command. The guns are fired along with a bugle call when a new commander-in-chief takes over or when a naval ship which has been out for a long time returns to the harbour.

Inside the edifice, artefacts of the colonial era such as ceramic bathtubs are stored. A maritime museum used to occupy some rooms in the past, but was shut down in 2000 and the exhibits moved to the decommissioned aircraft carrier INS Vikrant, which was subsequently opened to the public. A few ship ensigns still remain in the storerooms.

The islet is difficult to visit owing to the problems faced while berthing during low tide. The Navy has been offered many lucrative deals for the obsidian isle, but refuse to sell it as it is an important part of the Navy's heritage.