As a result, the midget program's focus changed to the infiltration of enemy harbours, where they would attack vessels at anchor. This concept failed completely during the attack on Pearl Harbor, where the midgets had no effect, and tying up 11 large submarines for six weeks in support of further midget submarine attacks on Sydney and Diego Suarez proved a waste of resources. Moreover, the failures at Sydney Harbour and Diego Suarez demonstrated that the improvements to the midget submarines made after Pearl Harbor had not increased the overall impact of the midget program. The modifications had various effects. The ability to man and deploy the midgets while the mother ships were submerged prevented the Army coastal radars from detecting the mother submarines. However, the midgets were still difficult to control, unstable, and prone to surfacing or diving uncontrollably. Beyond the use of the unreliable midgets, historians have identified areas in the plan of attack where the Japanese could have done significantly more damage. If the Japanese midget submarines had conducted a simultaneous, co-ordinated attack, they would have overwhelmed the defences. A chance for more damage came following the destruction of Kuttabul, when several naval vessels headed to sea, including USS Chicago, USS Perkins, Dutch submarine K-IX, HMAS Whyalla, and HMIS Bombay. The five mother submarines were already en route to the Port Hacking recovery position, and although Sasaki's plan at Pearl Harbor had been to leave some submarines at the harbour mouth to pick off fleeing vessels, he did not repeat this tactic. USS Chicagos survival Several factors beyond the control of any of the combatants contributed to the survival of USS Chicago. At the time of M-24s attack on Chicago, the latter had spent some time preparing to depart from Sydney Harbour, and although still moored and stationary, was producing large volumes of white smoke as the boilers warmed up. This smoke, streaming aft under the influence of the wind, and contrasting against the dark, low-lying cloud, may have given the impression that Chicago was moving, causing M-24 to lead the target when firing its torpedoes, and consequently sending its torpedoes across the bow. Another factor that may have influenced Chicagos survival was the extinguishing of Garden Island's floodlights minutes before M-24 fired its first torpedo, impeding targeting. Bombardment impact The bombardments failed to cause significant physical damage, but had a major psychological impact on the residents of