One of the procedures of the submarine that I enjoy very much is the ascent. Before ascending the Captain releases high pressure air from the submarine. When the high pressure air is released the submarine is usually in at least 2 atmospheres of pressure. Insided the submarine it is always at 1 atmosphere so there never is any pressure change that often occurs in an airplane. When the high pressure air is first released, the bubbles are very small but as they ascend they become 2 to 3 times bigger because of the increase of volume. Once the bubbles reach the surface the Captain of the shuttle boat sees them and then know where the submarine is at. If the surface is all clear then the Captain tells the Submarine Captain by way of the Underwater Telephone that it is safe to surface. Sometimes other boats are in the area and the submarine has to wait for getting clearance. If clearance is given right away then the submarine starts the ascent and it goes so fast that it actually passes the bubbles so that if one sees them it looks like they are sinking!