The Royal New Zealand Navy (RNZN; Māori: Te Taua Moana o Aotearoa, lit. ‘Sea Warriors of New Zealand’) is the maritime arm of the New Zealand Defence Force. The fleet currently consists of nine ships. The Navy had its origins in the Naval Defence Act 1913, and the subsequent purchase of the cruiser HMS Philomel, which by 1921 had been moored in Auckland as a training ship. A slow buildup occurred during the Interwar period, and then perhaps the infant Navy’s most notable event occurred when HMS Achilles fought alongside two other Royal Navy cruisers at the Battle of the River Plate against the German ship, Graf Spee, in December 1939.