The regiment crossed the Franco-Belgian border on 6 August and took part in the operations around Florenville. It also took part in engagements of the Great Retreat and the following Race to the Sea. At this early stage in the war it was still a horse-mounted formation wearing the plumed helmets and cuirasses of the Napoleonic period, with the colorful uniforms of peacetime. From November 1914 to March 1918 the 3rd Cuirassiers saw spells of service as temporarily dismounted "cuirassiers a' pied" in the trenches, in the North, the Somme, and Champagne. Except for these brief intervals, the 3rd retained its historic role as mounted heavy cavalry for most of the war, remaining in reserve behind the lines. Five of the other cuirassier regiments were fully converted to infantry after the opening stages of conflict.