Patrolling the Irish Sea out of Queenstown, Ireland, Conyngham made several rescues of passengers and crew from ships sunk by U-boats.

The General Board of the United States Navy had called for two anti-aircraft guns for the Tucker-class ships, as well as provisions for laying up to 36 floating mines.

[1] On 24 April 1917 Conyngham sailed from Boston, Massachusetts with her division for Queenstown, Ireland, the first destroyers to join English forces for duty after the entry of the United States into World War I earlier that month.

When the British ship Karina was torpedoed and sunk by German submarine UC-75 on 17 August 1917,[8] Conyngham sped to her assistance and rescued 39 survivors.

[1] The British Armed merchant cruiser Orama and ten destroyers, including Conyngham, were escorting an eastbound convoy of twenty steamers on 19 October, when German submarine U-62 surfaced in the midst of the group.

Lookouts on Conyngham saw U-62's periscope and quickly launched a depth charge attack on the spot where the U-boat had submerged, bringing oil and debris to the surface.

[10] After the hostilities had ended on 11 November 1918 with Germany signing the Armistice, Conyngham sailed from Queenstown on 14 December 1918 for Boston to have an overhaul.

She returned to Newport, Rhode Island, for summer exercises with her squadron and, after wintering at Charleston, South Carolina, reported to Philadelphia Navy Yard in March 1922 for inactivation.

The Treasury Department eventually determined that the United States Coast Guard simply did not have the ships to constitute a successful patrol.

To cope with the problem, President Calvin Coolidge in 1924 authorized the transfer from the Navy to the Coast Guard of twenty old destroyers that were in reserve and out of commission.

Designated CG-2, Conyngham was commissioned on 8 March 1925,[4] and joined the "Rum Patrol" to aid in the attempt to enforce prohibition laws.

[1] After the United States Congress proposed the Twenty-first Amendment to end prohibition in February 1933, plans were made for Conyngham to be returned to the Navy.