Lang departed New York 12 August 1939 guarding President Franklin D. Roosevelt's passage to Campobello, Newfoundland and Nova Scotia.

Transferred to the Pacific, she reached San Diego 18 March 1940 and Pearl Harbor 2 April, where she participated in fleet training exercises.

In December she acted as screen and aircraft guard during flight operations for Yorktown and Ranger off the Maine coast and Bermuda.

The destroyer then became a part of Force "W", sailing between England and the Mediterranean to deliver Spitfires to the besieged island of Malta (see Operations Calendar and Bowery).

As flagship for DesDiv 15, part of TF 18, Lang departed San Diego 1 July to join shore bombardment exercises off Tonga in preparation for the Guadalcanal-Tulagi landings.

The ships completed their mission and sailed for Purvis Bay, located in the Nggela Islands, part of the Solomon Islands from which Lang and two other destroyers escorted five LCIs to the landings at Onaiavisi, New Georgia, on 31 July, where during an enemy air attack Lang claimed an aircraft shot down.

Lang', in company with five other destroyers, was tasked to intercept enemy forces in Vella Gulf, part of the “Tokyo Express” route.

She departed the battle area for Manus on 31 October and on Christmas Day sailed with TF 78 for the Lingayen Gulf landings, where she was attacked by kamikazes and claimed another aircraft destroyed.

Lang departed the Pacific area of operations in June and arrived in San Francisco 3 July for repairs.