Visitors to the National Mall this weekend will encounter a wall of bright red poppies, installed to commemorate the men and women who have died in uniform in the century since World War I.Retired Navy Vice Adm. John Bird tells NPR the project uses 645,000 synthetic flowers — one for each American killed in an international conflict since the start of World War I — pressed against acrylic panels, which are backlit for dramatic effect."What we hope to do is have people take a moment on Memorial Day and this weekend to stop and reflect on the incredible sacrifice of American men and women," said Bird, senior vice president for military affairs at the United Services Automobile Association. The USAA — a San Antonio-based insurance, banking and insurance network for military members — created the exhibit.The wall of poppies includes an exhibit on the origin of the flower as a sign of fallen soldiers. Canadian military doctor John McCrae was the first to draw the connection, Bird said, with his 1915 poem In Flanders Fields: