Aviation is generally divided into three time periods, and those periods characterize its progress: Pioneer Period (to 1918), Development Period (to 1945) and the Modern Period (since 1945).
The Pioneer Period takes aviation from its inception through World War I. It includes early balloon flights, the development of lighter-than-air airships, early gliders, and the invention and early development of powered, controlled, heavier-than-air flight—the airplane.
Most airship development during the Pioneer Period aimed to achieve a design with practical application—i.e., an airship that was safe and reliable for passenger travel. The only successful development was the zeppelin airship in Germany, first flown on July 2, 1900. The airship generated enough public enthusiasm and financial support to overcome initial shortcomings. Business evolved rapidly, leading to the creation of the world's first airline – Delag – in 1910. Several zeppelin airships operated flights between various cities in Germany. The inception of World War I in 1914 intervened and ended the commercial operations, but the airship had proven itself. Zeppelin airships were made in substantial numbers for the German army and navy, used as both observation aircraft and bombers. The parallel and more rapid development of the airplane during the war period made the zeppelins vulnerable, however, and losses escalated.
Zeppelin airships carried a limited amount of mail during the Pioneer Period. During the pre-war period, mail was prepared by airship passengers and crew members. Much of this mail was given distinctive markings verifying it had been flown on a zeppelin. These items now represent the documentation of that period and those particular flights. The World War I-period mail from the military zeppelin units attests to that time.