The fourth USS Chicago is the Navy's 34th Los Angeles-class nuclear-powered attack submarine. She was christened by Mrs. Vicky Ann Paisley, wife of former Assistant Secretary of the Navy Melvin R. Paisley and launched on October 13, 1984. SSN 721 was commissioned on September 27, 1986, Cmdr. Robert Avery in command.

July 22, 2002 Cmdr. Craig M. Selbrede relieved Cmdr. Daniel E. Prince as commanding officer of USS Chicago during a change of command ceremony held onboard the submarine in Naval Station Pearl Harbor.

November 15, SSN 721 is currently participating in ANNUALEX 14G, a large bilateral maritime exercise Nov. 11-22, off the coast of Japan.

May 6, 2003 USS Chicago returned to Pearl Harbor following a routine six-month deployment, patrolling the U.S. 7th Fleet area of operations.

June 30, 2004 Cmdr. Rich Wortman relieved Cmdr. Craig Selbrede as CO of USS Chicago in a change of command ceremony at the Pearl Harbor Naval Station submarine piers.

February 4, 2005 SSN 721 arrived in Bremerton, Washington, for a scheduled availability period conducted by the Bangor Intermediate Maintanance Facility and the Pudget Sound Naval Shipyard.

November 29, USS Chicago departed Naval Station Pearl Harbor on a western Pacific deployment in support of the Global War on Terrorism.

May 30, 2006 The Los Angeles-class nuclear-powered attack submarine returned to homeport after steaming 30,514 nautical miles during a six-month underway period in the Western Pacific. During the deployment, the submarine's crew visited Hong Kong, Japan, Singapore and Guam.

On July 25, 28 ships and submarines, including SSN 721, concluded the Exercise Rim of the Pacific (RIMPAC) 2006. Eight nations participated in RIMPAC, the world's largest biennial maritime exercise. Conducted in the waters off Hawaii, RIMPAC brings together military forces from Australia, Canada, Chile, Peru, Japan, the Republic of Korea, the United Kingdom and the United States.

August 11, Rear Adm. Joseph Walsh relieved Rear Adm. Jeffrey Cassias as commander, Submarine Force, U.S. Pacific Fleet
(COMSUBPAC), in a change of command ceremony aboard USS Chicago.

November 9, The Los Angeles-class attack submarine is currently participating in the Joint Task Force Exercise (JTFEX) off the coast of Southern California, with the USS John C. Stennis Strike Group (JCSSG), in preparation for their upcoming deployment.

June 27, 2007 SSN 721 pulled to Yokosuka, Japan, for a scheduled port visit.

January 6, 2009 USS Chicago departed Pearl Harbor for a six-month western Pacific deployment.

June 29, The Chicago returned to homeport after a scheduled underway period.

August 7, Cmdr. Jeffrey L. Cima relieved Cmdr. Rick J. Stoner as CO of USS Chicago during a change-of-command ceremony held at Naval Station Pearl Harbor.

March 15, 2010 Capt. Daryl Caudle, commander of Submarine Squadron 3, fired Cmdr. Jeff Cima after he was found guilty of "drunkenness" and "conduct unbecoming an officer," in nonjudicial punishment. The squadron’s deputy commander, Capt. James Horten, has temporarily taken command of SSN 721.

July 8, Cmdr. Nicholas R. Tilbrook relieved Capt. James Horten as CO of the Chicago during a change-of-command ceremony aboard USS Missouri Museum at Joint Base Pearl Harbor-Hickam.

October 27, Pearl Harbor Naval Shipyard successfully undocked USS Chicago from its scheduled engineered refueling overhaul, six weeks ahead of schedule.