Sydney's defences were expanded following the withdrawal (Cardwell Reforms) of British soldiers from Australia during the 1870s. This prompted the construction of four sets of fortifications on Georges Heights and around other parts of the harbour, the Middle Head Fortifications, the Georges Head Battery, and a smaller fort located on Bradleys Head were constructed during this period and upgraded in the 1880s on the advice of British experts. They were designed to attack enemy ships as they attempted entry into Sydney Harbour. Some of these forts were, at the time, built of an out dated design.