The light cruiser St Louis was laid down by Newport News S.B.Co. on 10 December 1936 and completed in December 1939. She was sister ship to Helena. Her displacement was 9,700 tons, her length overall 609 feet and beam 62 feet. She was armed with fifteen 6-inch, 47 caliber and eight 5-inch, 38 caliber guns as well as 16 40mm and 24 20mm anti-aircraft guns. She carried four aircraft and her complement was between 888 and 1,200 men. On 7 December she was moored in the most easterly of the docks at the Navy Yard, with two boilers dismantled and with water and electricity supplied from ashore. Her captain, George Rood (Rood, George), had these connections cut and the hole in the side of the ship hurriedly welded up when the Japanese attacked. He got his command under way during the Second Attack Wave at about 0930 and made all speed for the entrance of Pearl Harbor. The hazard of midget submarine attack in the entrance channel was met by high speed; two torpedoes missed. In the late morning her gunners opened up on aircraft (probably American) twice, but without doing damage. St Louis briefly joined Detroit as part of a force under Rear Admiral Milo Draemel, but this soon broke up when, at 1205, a signal from CinCPAC sent her in search of enemy vessels five miles south of Barber's Point, the south-western extremity of Oahu. Fortunately Rood recognized the supposed target as Minneapolis before harm was done.
You can find out more about the St Louis in the following Osprey book: