loop undetected at 21:48, and at approximately 22:00 followed a Manly ferry through the anti-submarine net. At 22:52, M-24 was spotted by a Chicago searchlight operator less than to the moored cruiser's starboard, and on a course roughly parallel to the ship's facing. Chicago opened fire with a gun and a quadruple machinegun mount, but inflicted minimal damage as the weapons could not depress far enough. Some of the shells skipped off the water and hit Fort Denison's Martello tower, while fragments were later found in the suburbs of Cremorne and Mosman. The senior officer present aboard Chicago ordered the crew to begin preparing for departure, and for USS Perkins to begin an anti-submarine screening patrol around the cruiser, orders that were revoked by the sceptical Captain Howard Bode when he arrived on board at around 23:30. and also fired upon M-24 as it fled west toward the Sydney Harbour Bridge, before the midget was able to submerge and escape. When it returned to periscope depth, the midget found itself west of Fort Denison. It turned and sailed east for about , then took up a firing position south-west of Bradley's Head, from where its commander could see Chicagos stern silhouetted against the construction floodlights at Garden Island's new Captain Cook Graving Dock. Midget submarine M-21—from I-22—probably entered the harbour at the same time that USS Chicago opened fire on M-24. The unarmed Naval Auxiliary Patrol boat Lauriana (later commissioned HMAS Lauriana) spotted M-21 and illuminated the submarine's conning tower, while sending an alert signal to the Port War Signal Station at South Head, and the nearby anti-submarine vessel HMAS Yandra. Yandra attempted to ram the submarine, lost contact, regained contact at 23:03, and fired a full pattern of six depth charges. At the time of the attack, it was assumed that the depth charges had destroyed or disabled the midget, but M-21 survived. Historians believe that the midget took refuge on the harbour floor and waited until the Allied vessels had moved away before it resumed the attack. At 23:14, Muirhead-Gould ordered all ships to observe blackout conditions. Just after 23:30, he set off on a barge towards the boom net, to make a personal inspection. The Admiral reached Lolita at about midnight and indicated to her crew that he did not take the reports of enemy submarines seriously, reportedly saying: "What are you all playing at, running up