A recent television documentary on the German airship Hindenburg began with the announcement that it would first explore the history of "dirigibles, known as Zeppelins" - a typical example of the welter of ignorance and confusion into which the terminology of lighter-than-air flight has fallen. This article will attempt to sort out the semantic muddle, for an understanding of the terms in its title can be important to an understanding of some aerial aspects of the Great War.

There are two forms of lighter-than-air-craft the balloon and the airship; the generic term for both is aerostat. Both are able to ascend into the sky and stay there because they contain a substance that is lighter than the air that surrounds them.

Hot air was the balloon's first lifting substance, but is limited flight time because of the simple fact that heated air will eventually cool. Sustained hot-air ballooning did not become feasible until after World War II with the innovation of the propane burner, which permits reheating while the craft is aloft.

For more than a century the principal and preferred lifting substance for both balloons and airships was hydrogen, the lightest of the elements, despite it being highly dangerous because of its extreme flammability. It was not succeeded by helium (which although somewhat inferior to hydrogen in lifting strength will not burn or explode) until a crash American research program beginning in 1917 developed means of extracting it cheaply in large quantities from the natural gas in which it is found. Today the aeronautical employment of helium is slight, but is has host of important industrial, scientific and medical uses.

The fundamental difference between the airship and the balloon is that the former is powered and horizontally controllable and the latter is neither. The altitude of a free-floating balloon can be regulated to a considerable degree by dropping ballast and venting gas, but its horizontal direction is determined solely by which way the prevailing wind blows it. It is therefore incorrect to refer to balloonists, as modern journalists so often do, as "pilots" - a balloon cannot be piloted in any sense of the word.

Add propulsion and control to a balloon and you have an airship, the first four crude examples of which flew in France if only haltingly and briefly between 1852 and 1884, decades before the Wright brothers created the first verifiably successful powered heavier-than-air flying machine. ¹

The French connection is how and why the word "dirigible" entered English as a synonym for "airship." It comes from the French word dirigeable the adjectival form of the transitive verb diriger, which means, among other things, to control or steer. Thus, with incontestable Gallic logic, a steerable lighter-than-air craft was called a ballon dirigeable. Eventually ballon was dropped and the adjective became the noun; thus dirigeable remains to this day the French term for airship. It was the same process by which cuirasse from vaisseau cuirasse (literally "armored ship") became the French term for battleship.

Like so many French aeronautical coinages (aileron, fuselage, nacelle, hangar, even the very word aviation itself), the French term, with a change in spelling, entered English as "dirigible balloon." And again, the adjective eventually became the noun but it was not in widespread use until after the Great War. The preferred word was airship, which replaced the cumbersome "dirigible balloon." The exact same word was adopted in German - Luftschiff (luft: air; schiff: ship).

Dirigible as a synonym for airship is actually a misnomer. Since dirigible means, as noted above, simply "steerable," it can logically be applied to any device whose direction can be controlled by human agency even a bicycle. In scientific usage, however, it has been restricted to aeronautical application; anything from a kite to a jetliner can be called "dirigible." (This restriction was not always the case; in the early stages of naval torpedo development the type that was controlled by unreeling wire was sometimes termed dirigible.)

By the start of the Great War the airship had been developed into two main types - rigid and non-rigid (technically, the latter is more accurately described as pressure-rigid). Cylindrical in cross-section, both were given buoyancy by gas and motion by engine-driven propellers and were controlled by vertical rudders and horizontal elevators.

In the rigid type, a solid framework, which might be likened to a skeleton, supports an external covering of fabric called the envelope (a very few experimental types had a metallic covering). Within the framework are contained bags of gas called balloonets. In the non-rigid, the envelope's shape is maintained by the pressure of the gas that fills it; there is no framework. The rigid's control car and engines are suspended from the framework; in the non-rigid they are attached directly to or suspended directly from the envelope. (In some later rigids the engines were mounted internally, driving the propellers by transmission belts.)

There was an intermediate type, now long vanished, called the semi-rigid. It had a pressure-rigid envelope but a solid keel.

The rigid airship, employed so extensively by Germany during the Great War, was perfected soon after the turn of the century by a former Wurttenberg army cavalry officer, Ferdinand Adolf August Heinrich Graf von Zeppelin, who had been inspired by a balloon ascent he had made in the United States on 19-Aug-1863. ² His craft were, naturally , known as Zeppelins. "Zeppelin" is a proprietary, or trade, name (such as Kodak, Ferris Wheel and Autogiro), and is applied properly only to craft constructed by Luftshiffbau Zeppelin G.m.b.H. or firms licensed to use its patents. It should thus be spelled with a capital Z; modern writers who spell it in lower case are mistaken in their apparent belief that it is generic. ³

It has become customary to refer to all German rigid airships of the Great War as Zeppelins, but in fact not all were. Some were constructed by a rival firm, Luftschiffbau Schutte-Lanz G.m.b.H., which employed a framework of laminated plywood instead of the aluminum alloy used in Zeppelins. ⁴

The vast amount of literature devoted to German airships can easily, and has, led to the belief that these were the dominant LTA craft of the Great War. Actually, the British navy was the greatest exponent of the airship, receiving more than 200 non-rigids during 1915-1918 for anti-submarine patrolling. This type was also used, although in far fewer numbers, by the U.S. Navy and the French and Italian armies and navies. The German army and navy also had a handful.

The rigid airship no longer exists; none has been built since the 1930s. ⁵ The demise is usually blamed on the Hindenburg disaster ⁶ although that had been preceded by the loss of a number of American, British, French and Italian rigids. All airships flying today are non-rigid types, popularly known as blimps.

A number of theories have been advanced concerning the etymology of "blimp," but in fact it is an onomatopoeic word whose coinage can be traced specifically to 5-Dec-1915 when Royal Naval Air Service Lieutenant A. D. Cunningham playfully flicked a finger against the envelope of SS. 12 at the Capel air station and then mimicked aloud the sound It had made.

"Blimp," then, is essentially a slang term, although it was given one official cachet in Jul-1943 when the U.S. Navy, the only service in the world to operate airships during World War II, inexplicably changed the designation "airship patrol squadron:" to "blimp squadron."

Modern airships serve a number of utilitarian functions, but they remain relative oddities in the sky and are generally known only as flying billboards and for flashing advertising messages and transmitting television images of sporting events. And modern media ignorance of lighter-than-air history has resulted in the distortions of its nomenclature that I hope this article will help rectify. ⁷

Space precludes a list of sources, but I will be glad to supply a bibliography to anyone interested.