cruiser HNLMS Tromp, Australian destroyer and US destroyer , searched unsuccessfully for the submarine. Muirhead-Gould concluded that the submarine had operated alone and had left the area immediately after the attack. I-29s floatplane made a reconnaissance flight over Sydney on 23 May. A secret radar unit set up in Iron Cove detected the flight, but authorities dismissed its report as a glitch, as there were no Allied aircraft operating over Sydney. The aircraft was damaged or destroyed on landing, although its two crew survived. They reported the presence of several capital ships, including two battleships or large cruisers, five other large warships, several minor war vessels and patrol boats, and prolific merchant shipping. The report, which the Allied FRUMEL signals intelligence network partially intercepted, resulted in the Japanese Navy selecting Sydney as the target. The three midget-carrying submarines rendezvoused with I-29 and I-21 approximately north-east of Sydney Heads, with all five submarines in position by 29 May. Midget submarine operation Final reconnaissance Before dawn on 29 May, I-21s floatplane, piloted by Ito Susumu, performed a final reconnaissance flight over Sydney Harbour, with the mission of mapping the locations of the major vessels and of the anti-submarine net. Multiple observers spotted the floatplane but assumed it was a US Navy Curtiss Seagull. No alarm was raised until 05:07, when it was realised that the only ship in the area carrying Seagulls was the U.S. cruiser Chicago, and all four of her aircraft were on board. Richmond Air Force Base launched Wirraway fighters, which failed to locate I-21 or the floatplane. Therefore, the reconnaissance flight did not result in the authorities in Sydney taking any special defence measures. The floatplane was seriously damaged on landing and had to be scuttled, but both aircrew survived. Plan of attack The Japanese planned to launch the midgets one after the other between 17:20 and 17:40, from points outside Sydney Harbour. The first midget was to pass through the Heads just after 18:30, but heavy seas delayed her by over an hour. The other two midgets followed at twenty-minute intervals and were similarly delayed. The choice of targets was left up to the midget commanders, with advice that they should primarily target aircraft carriers or battleships, with cruisers as secondary targets. The midgets were to operate to the east of the Harbour Bridge, although if no suitable targets were to be found in this area they