I received this Official Postcrossing card from California! Depicted are two US Navy airships that existed between the World War eras: USS Akron and USS Macon. These airships, which were sister vessels to each other, were first launched in 1931, and were the largest aircraft of their time. Let’s talk a bit about airships: airships are aircraft that use gases that are lighter than air to ascend. During the early years, it was customary to use hydrogen to achieve this, however when the Hindenburg airship caught fire and was destroyed in 1937, a switch to helium was made. So the way that airships achieve their ascent and descent comes from the manipulation of air pressure and helium pressure using these tanks called ballonets. When they launch, they let out air from the ballonets, causing the helium to kind of overtake it and thus make the ship buoyant. Then when they wanna land, they fill them with air, causing the airship to be denser, to the point where the helium isn’t enough to keep it afloat. While airships are not very common anymore, you might see them in the form of blimps, which are often used for advertising. The main difference between blimps and airships like the USS Akron and USS Macon is that the former are non-rigid airships, and the latter are rigid airships. A rigid airship just means that it has a skeleton or internal frame. Also, where blimps are dependent upon the gas pressure to keep their shape, rigid airships always keep their shape, thanks to these frames. One thing that sets the USS Akron and USS Macon apart from many other airships is that they were able to launch and retrieve smaller aircraft in midflight. Imagine – having enough lighter-than-air gas to hold planes and still be floating! I can only imagine the precision needed to balance the air-to-helium ratio when sending and receiving aircraft. (Oh, and I should mention that these two airships were helium-based, despite hydrogen being used for other airships at that time). Unfortunately, both airships tragically crashed due to poor weather conditions, just a few years after their first flights. While we don’t see these kinds of aircraft much anymore, they remain a pretty unique entity in the history of transportation. Thank you so much for sending me this postcard!