 Most planning focused on the first phase , which was seen as the most critical . This phase involved construction of defence works for Singapore . For the second phase , a naval base capable of supporting a fleet was required . While the United States had constructed a graving dock capable of taking battleships at Pearl Harbor between 1909 and 1919 , the Royal Navy had no such base east of Malta . In April 1919 , the Plans Division of the Admiralty produced a paper which examined possible locations for a naval base in the Pacific in case of a war with the United States or Japan . Hong Kong was considered but regarded as too vulnerable , while Sydney was regarded as secure but too far from Japan . Singapore emerged as the best compromise location . 
