Weekly Questions Thread #56: Now with minor rules updates

I'm attempting to come up with several different types of "ships", each based on one of the four elements. For a bit of preface, the material world has one large continent (plus islands, large lakes within the continent, etc.) where my campaign is mainly taking place, and the empire is divided into four kingdoms (earth, fire, air, water) each with a king and/or queen; at the center of the continent is where the emperor resides. The way this world works, is that the elements are very prevalent in each kingdom, and areas in between kingdoms are a mishmash of elements (desert in the middle of air and earth kingdoms, swamps between earth and water, etc.), with the emperor's territory in the middle being quite chaotic and sporadic and fantastical.

So, each kingdom has developed their own method of transportation with a fusion of the material, and the magical. Air ships use special crystals that give the ships the power of flight and mobility; water ships utilize steam power and have Navimancers (mages who work on enhancing boats and other related things) to enhance the hull so they can move freely through ice as well as float and move safely on shallow waters; and terrain ships (trains... Haha...) are essentially wider trains that travel across railroads, the railroads are enhanced and are invisible, can be moved through the ether short distances to change final destination, and can be lifted miles in the air to bypass dangerous areas... The carts of the terrain ship are similarly enhanced to travel through earth, allowing these ships to sail straight through mountains. However, I'm having a bit of trouble coming up with a fire ship. I was considering having the "ships" be smaller in size (jeeps, motorcycles, fighter planes) and utilizing gun powder somehow for the engine, and the other magical outlets that they have. They would be small, quick, and very versatile! I couldn't think of a feasible "fire" medium for the ships to travel through, other than having a very localized mode of travel near a volcanic island chain. The world exists in a steampunk-esque era, if that wasn't evident, where steam power and gunpowder is becoming more popular. Any tips on fire ships (or anything else!) would be greatly appreciated.

/r/DnD Thread