The firing arcs of the forward and aft batteries intersected at a very limited angle, giving her an arc of 60° in which she could fire all of her guns broadside (excluding the wing mounts). Because "Atlanta" was able to bring all her guns to bear only within that narrow arc, her ability to engage surface targets was limited. Her firing arcs were ideally suited to bringing her guns to bear on an aircraft, however, with a minimum of six guns available from any angle. After fitting out, "Atlanta" conducted shakedown training until 13 March 1942, first in Chesapeake Bay and then in Maine's Casco Bay, after which she returned to the New York Navy Yard for post-shakedown repairs and alterations. Adjudged to be "ready for distant service" on 31 March, the new cruiser departed New York for the Panama Canal Zone on 5 April. She reached Cristobal on 8 April. After transiting the isthmian waterway, "Atlanta" then cleared Balboa on 12 April with orders to reconnoiter Clipperton Island, a tiny barren, uninhabited atoll about 670 mi (1,080 km) southwest of Acapulco, Mexico, in the course of her voyage to the Hawaiian Islands, for any signs of enemy activity. Finding none, she ultimately reached Pearl Harbor on 23 April. Punctuating her brief stay in Hawaiian waters with an antiaircraft practice off Oahu on 3 May, "Atlanta", in company with , sailed on 10 May as escort for and , bound for Nouméa, New Caledonia. On 16 May, she joined Vice Admiral William F. Halsey's Task Force 16 (TF 16), formed around the aircraft carriers and , as it steamed back to Pearl Harbor, having been summoned back to Hawaiian waters in response to an imminent Japanese thrust in the direction of Midway Atoll. TF 16 arrived at Pearl on 26 May. "Atlanta" again sailed with TF 16 on the morning of 28 May. Over the days that followed, she screened the carriers as they operated northeast of Midway in anticipation of the enemy's arrival. At the report of Japanese ships to the southwest, on the morning of 4 June, "Atlanta" cleared for action as she screened "Hornet". Squadrons from the American carriers sought out the Japanese, and during that day, planes from and "Enterprise" inflicted mortal damage on four irreplaceable enemy aircraft carriers. Japanese planes twice hit TF 17, and it took the brunt of the enemy attacks.