The first round parachutes were simple, flat circulars. These early parachutes suffered from instability caused by oscillations. A hole in the apex helped to vent some air and reduce the oscillations. Many military applications adopted conical, "i.e.", cone-shaped, or parabolic (a flat circular canopy with an extended skirt) shapes, such as the United States Army T-10 static-line parachute. A round parachute with no holes in it is more prone to oscillate and is not considered to be steerable. Some parachutes have inverted dome-shaped canopies. These are primarily used for dropping non-human payloads due to their faster rate of descent.