HMAS Adelaide was a Town-class light cruiser of the Royal Australian Navy (RAN), named after Adelaide, the capital city of South Australia. Laid down in 1915, wartime shortages and design modifications meant the ship was not completed until 1922, earning her the nickname "HMAS Longdelayed".

The Town class was a group of twenty-one light cruisers built for the Royal Navy (RN) and Royal Australian Navy (RAN) of the first half of the 20th Century. These vessels were long-range cruisers, suitable for patrolling the vast expanse covered by the British Empire. These ships, initially rated as second class cruisers, were built to a series of designs, known as the Bristol, Weymouth, Chatham, Birmingham and Birkenhead classes – all having the names of British towns except for the RAN ships, which were named after Australian cities.