In the late 1910s, attempts were being made to achieve higher and higher altitudes. In 1920, flights well over were first achieved by test pilot Lt. John A. Macready in a Packard-Le Père LUSAC-11 biplane at McCook Field in Dayton, Ohio. The flight was possible by releasing stored oxygen into the cockpit, which was released directly into an enclosed cabin and not to an oxygen mask, which was developed later. With this system flights nearing were possible, but the lack of atmospheric pressure at that altitude caused the pilot's heart to enlarge visibly, and many pilots reported health problems from such high altitude flights. Some early airliners had oxygen masks for the passengers for routine flights.