If it has dirigibles, it’s steampunk. No, that doesn’t quite work.
If it doesn’t have dirigibles, it isn’t steampunk. No, that doesn’t work, either.
If it is steampunk, then chances are, there’s a dirigible in it somewhere. OK, now there’s a pronouncement I feel comfortable with. Even Brisco County, Jr. had a dirigible eventually.
The variety of airships (a more generic term) in steampunk is huge, especially if you look at the vast number of illustrations on line. The Aurora in Oppel’s Ariborn is entirely realistic. The Predator in Butcher’s Aeronaut’s Windlass if essentially an air-floating wooden sailing ship. Some are essentially floating cities. Some run on diesels. Some run on magic, or crystal power.
Back here on Earth, everybody knows at least one dirigible, the Hindenburg, just like everybody knows at least one steam ship, the Titanic, and for essentially the same reasons. Beyond that, real knowledge of actual airships is spotty.
It might be helpful, before embracing the infinite variety of steampunk airships, to have a go at definitions for those which actually existed.
First up, why dirigible instead of Zeppelin? Answer: for the same reason that we use the word automobile instead of calling all automobiles, Fords. Ferdinand von Zeppelin meant more to the development of dirigibles than Henry Ford did to the development of autos, so if you want to say Zeppelin instead of dirigible, I won’t argue with you. After all, I used to say, “Gimme a Coke,” when I really wanted a Pepsi.
However, in the world of my upcoming steampunk novel, you wouldn’t dare say Zeppelin. It would be unpatriotic. A Brit with more ambition than morals stole Zeppelin’s plans, sabotaged his work, and built a British fleet of airships before the German war, while Zeppelin’s war efforts came to nothing. The result was a sweeping British victory, an overwhelmingly powerful Britain, and a very interesting world to write about. But no one calls dirigibles Zeppelins.
In our (real) world, airships are often divided into three classes, blimps, semi-rigids, and dirigibles. Blimps are bags of lifting gas which hold their shape entirely due to internal pressure. Pull the plug, and they collapse. Semi-rigids have a keel structure which helps to keep them from distorting due to localized weights, such as engines, but they still don’t have a solid skin. Dirigibles have a skeleton and a skin, and individual gas bags for the lifting gas. Dirigibles are sometimes called rigids; that is the most accurate term, but it is rarely used.
You will find this three part division in dozens of books on airships, and it fits pretty well. But the word dirigible was used far earlier, and at that time it meant “capable of self-movement and control”. There were dirigible torpedoes in the water, long before Zeppelin put dirigible airships into the air.
Which drags us back to another recycling of an old word — torpedo. During the American Civil War there were two types of torpedoes, stationary and spar. A stationary torpedo was a mine. When Admiral Farragut sailed into Mobile Bay, shouting, “Damn the torpedoes, full speed ahead,” that would translate into modern English as, “Damn the mines, full speed ahead.” A spar torpedo, on the other hand, was an explosive device attached to a long wooden pole and rammed into an enemy ship by a steam boat, often sinking both. Neither kind of torpedo had self propulsion or self steering.
Torpedoes with that capability were initially called dirigible torpedoes. The adjective dirigible was later dropped. E. E. Smith, in Triplanetary, recycled that old term for use in galactic warfare:
In furious haste the Secret Service men had been altering the controls of the radio-dirigible torpedoes, so that they would respond to ultra-wave control; and, few in number though they were, each was highly effective.
The original hot air balloons were (and still are) unable to steer or move on their own. The quest for dirigibilty (controlled self- movement) led to blimps, semi-rigids, and “dirigibles”.
So, there is plenty of confusion even before we get to the use of airships in steampunk. Call them dirigibles, if you want. Call them Zeppelins, if you want. I don’t see how anyone has a right to complain about your choice.