Civil War-era balloon replica on the National Mall in Washington

This 19,000-cubic-foot, netted gas balloon, seen partially inflated in near the US Capitol in Washington, DC, on June 11, 2011, was built in 1941 and is very similar in operation and size to the balloons used by Thaddeus Lowe in June 1861 to demonstrate to President Lincoln how a gas-filled balloon might be used to spy on the enemy-thus helping the Union Army and establishing the earliest "air force." UPI/Roger L. Wollenberg