While Wilcox was at the New York Navy Yard, the United States entered World War I on 6 April 1917.
He was promoted to lieutenant commander on 23 May 1917.
Late in 1917, he left the navy yard to became the first commanding officer of the armed yacht USS Yacona (SP-617) when she was commissioned on 10 December 1917 for World War I convoy escort and antisubmarine duty in the Atlantic Ocean.

By March 1918, Wilcox was flag secretary on the staff of Commander, Battleship Force 2, United States Atlantic Fleet, and he received the Navy Cross for distinguished service during that duty.
On 1 July 1918, he received a promotion to a temporary wartime rank of commander.
The war ended on 11 November 1918, and by the beginning of 1919, Wilcox was the executive officer of the troop transport USS Von Steuben (ID-3017), engaged in bringing American servicemen home from Europe in the immediate aftermath of the war.
While Wilcox was at the New York Navy Yard, the United States entered World War I on 6 April 1917. He was promoted to lieutenant commander on 23 May 1917. Late in 1917, he left the navy yard to became the first commanding officer of the armed yacht USS Yacona (SP-617) when she was commissioned on 10 December 1917 for World War I convoy escort and antisubmarine duty in the Atlantic Ocean.
By March 1918, Wilcox was flag secretary on the staff of Commander, Battleship Force 2, United States Atlantic Fleet, and he received the Navy Cross for distinguished service during that duty. On 1 July 1918, he received a promotion to a temporary wartime rank of commander. The war ended on 11 November 1918, and by the beginning of 1919, Wilcox was the executive officer of the troop transport USS Von Steuben (ID-3017), engaged in bringing American servicemen home from Europe in the immediate aftermath of the war.
John W. Wilcox Jr.