Airships

Airships are large aircraft, available from 1890.

Technical
Airships operate using hydrogen to generate buoyant lift. Originally powered by compact steam engines, modern versions are usually powered by light internal combustion engines, usually diesel.

Currently, the most common type of airship is the Humerlandic-built Leviathan-class, with over 3,700 built at the time of writing (all variants).

Application
Airships are usually used by the military. The most common purposes are roles such as bombing and reconnaissance. Humerlandic doctrine, and those influenced by it, maintains that there are four types to be used by the military:

Patrol Airships, used for naval patrol and anti-shipping duties, and fleet spotting. Has defensive machine-guns (maxims, originally gatlings), but generally main armament is bombs (5 tons usually). Operated by the navy.

Airships, Gunship, used for observation, close air support where possible, and tactical bombing. Typically armed with a large number of downward-facing machine-guns, plus bombs (usually 4 tons). Operated by the army.

Strategic Bomber Airships, used for strategic bombing of cities. Has defensive machine-guns, but generally main armament is bombs (up to 10 tons). Operated by air force. At a pinch, can be used for cargo transport or even rapid troop deployment.

Cruiser Airships (also called Airship Destroyers). Airships designed to knock other airships out of the sky. Armed with six machine-guns, which can fire incendiary bullets, plus a forward-facing limited-traverse 3-pounder gun. MGs are to be fired in a broadside, while the 3-pounder is to be fired immediately before ramming.

Non-Military
Humerland's Orient & Alituria line and Royal Mail have experimented with airship services to Alituria or even Australis, taking diplomatic mail, courier service, and passengers, taking just 3 days (35:12:55) to get there, on average. Due to start service in 1913, using war-surplus airships.