Portkil Battery (Portkil Point Battery, was built between November 1900 and March 1904 to mount two 6-inch BL guns and two 4.7-inch QF guns. The two sets of gun emplacements were in effect separate batteries, with underground magazine and crew shelters located between the gun emplacements. The two batteries were located adjacent to each other, some 150 metres apart.
Initial plans have been to arm the battery with 10-inch and 64-pdr RML, later amended to 9.2-inch and 6-pdr. By 1989 it was proposed that the site have a single 9.2-inch, two 6-icnh and two 4.7-inch. The final design saw the removal of the 9.2-inch gun. Portkil Battery sat across the River Clyde opposite to Fort Matilda. Ardhallow Battery lay some 5 kilometres to the West in a direct line across the River, but much further by road.
Defence Electric Lights were mounted on the shore line with an Engine Room to provide power. Blockhouses were later added to provide land defences.
The Battery remained in service during World War but had been disarmed in 1929 when the Clyde defences were concentrated at Ardhallow and Cloch Batteries. During World War 2 a new Battery was built at Toward Point with Rothesay Sound becoming the Examination Battery.