HMAS "Platypus" was a submarine depot ship and base ship operated by the Royal Australian Navy (RAN), ordered prior to World War I to support the Australian submarines originally known as just AE1, HMAS "AE1, was an "E"-class submarine of which organization?
HMAS Platypus (1917):  Ordered prior to World War I to support the Australian submarines "AE1" and "AE2", "Platypus" was not completed until after both submarines had been lost, and she was commissioned into the Royal Navy from 1917 to 1919. HMAS AE1: HMAS "AE1 (originally known as just AE1") was an "E"-class submarine of the Royal Australian Navy (RAN).
Royal Australian Navy (RAN)