When war broke out in 1914, he commanded the 3rd Regiment of Foot Soldiers in Tournai. He was wounded twice in October 1914: first during the evacuation of Antwerp and later during the Battle of the Yser at Pervijze. Major General Rucqouy became commander of the 5th Army Division in 1915. On 6 January 1917, he succeeded General Wielemans as Chief of Staff of the Belgian Army. He held this post until April 1918, after which he returned to the front at his own request as commander of the 5th Army Division. He preferred direct command of troops in the field to an administrative and strategic role at headquarters.
The 5th Army Division was involved in the recapture of strategic points in the Westhoek, which paved the way for the advance to the east. The unit drove the German troops back across the Leie and the Scheldt in the weeks before the Armistice.
After the Armistice, he became commander-in-chief of the Belgian occupation army in Germany.
