After shakedown out of Bermuda, British West Indies and Norfolk, Virginia "O'Brien" joined convoy forces 14 May 1944 en route to Scotland and England. Following patrol and escort duty near England, she participated the invasion of Normandy and in-shore Bombardment of Cherbourg. On 25 June while supporting minesweepers well inshore of the battleship , which was engaging German shore batteries at Cape Levi, near Cherbourg, "O'Brien"s own gunfire was so accurate that enemy gunnery positions shifted from "Texas" to "O'Brien". She received a direct hit just abaft the bridge, but was able to stay on station long enough to lay a smoke screen for "Texas". Thirteen men were killed and nineteen wounded. Following temporary repairs on the Isle of Portland, England, "O'Brien" escorted a convoy to the Boston Naval Shipyard where she underwent extensive work.