On 29 May 1942 five large Japanese I Class submarines rendezvoused some 35 nautical miles northeast of the entrance to Sydney Harbour. Before daylight the next morning an E14Y Glen float plane launched from one of the submarines, I-21, and crewed by Warrant Flying officer Susumo Ito and Ordinary Seaman Iwasaki, flew a daring reconnaissance mission over the harbour, twice circling the cruiser USS Chicago before flying off to the east.
The aerial intrusion was observed and reported but it did not initiate any special harbour defensive measures being implemented. Many mistakenly believed it an American floatplane conducting a routine training flight. For the Japanese raiders, it was the latest of a number of reconnaissance flights conducted over Sydney providing valuable intelligence for an impending surprise attack on the numerous Allied warships anchored peacefully in the harbour. Prime targets included the cruisers HMAS Canberra and USS Chicago.
