The advent of World War I had a significant impact on the construction of Memorial Amphitheater. The United States entered the war in April 1917, and by spring 1918 American troops were arriving in Europe. Most skilled workers were diverted to the war effort, although artisans (such as marble carvers) were still available. The Corps of Engineers was able to obtain, after lengthy delays, the high-quality marble it needed for the approaches from the island of Vinalhaven, Maine. But railroads and cargo ships were so congested carrying war materiél and military personnel that the marble could not be transported to Arlington National Cemetery until late 1917. By then, another severe winter had set in. Intensely cold weather continued into the late spring, further delaying work. Only a limited amount of work on the approaches had concluded by the end of June 1918. Some modifications were also made to the structure because of the war. The largest of these changes eliminated the seating planned for the top of the colonnade.