To most people the giant airships known as Zeppelins are nothing more than memories from the 1930s, but they may be making a comeback. Several large aeronautics companies are designing modern airships that could carry huge loads of cargo with just a fraction of the fuel used by airplanes. Airships need relatively little fuel to take off or to propel themselves, and that makes them a much more carbon-efficient way to move air cargo - which is set to triple in the coming decades. In addition to fuel efficiency, airships have other potential advantages. They take off and land more like a balloon than an airplane, thus making it easier to deliver cargo when there is no landing strip and/or poor infrastructure. They would also be ideal for large bulky cargo which could be carried underneath using cables.

The designers of these new vehicles have a choice as to which gas to use for buoyancy - hydrogen or helium. Hydrogen has major advantages in that it is inexpensive, can be created using renewable energy and has about 7% greater lifting ability than helium. The downside is that hydrogen is flammable whereas helium is not, so most companies are planning to use helium for extra safety. The airships that are being developed now are called hybrids as they blend lighter-than-air travel with some aspects of fuel-powered boost. These will attain speeds that are about two times as fast as cargo ships. Future models may be able to fly much higher and faster by taking advantage of the free winds of the jet stream - the narrow band of fast-moving air above the troposphere. These winds average 200 km per hour, and could propel an airship at much greater speed with almost no use of fuel.