ZMC-2

The only metal-skinned airship ever flown was built at Grosse Ile, Michigan in 1929, and was operated by the US Navy until her scrapping in 1941. You can read more about the ship here:
ZMC-2

Aerospace aluminum alloys are immensely strong and not very dense, which makes them ideal for applications where strength without (much) weight is essential. Unfortunately many alloys, particularly early in the history of metal aerospace structures, suffer from corrosion problems over the service life of an aircraft. Pure elemental aluminum has fantastic corrosion resistance, not because it resists oxidation, but because a thin layer of aluminum oxide (or corundum if you're into fancy mineral names) quickly forms on any exposed aluminum surface, and this coating is chemically identical to the stuff that sapphires and rubies are made of. Rather than flaking away as rust, weakening the structure as iron oxide does to steel, a little corundum goes a long way to protecting aluminum from the elements. Given the strength of aluminum alloyed with elements like copper, magnesium, and silicon, and the corrosion-resistance of pure aluminum, metallurgists developed a method in the 1920s to place a thin aluminum layer atop alloy plate without leaving behind a weak bondline. The result was alclad, and ZMC-2 was the first full-scale demonstration of an aircraft built with this technique.

In addition to the innovation in the material that composed her, ZMC-2 broke new ground in her structure. The orthodox way to build a zeppelin was to place bags of lifting gas in a metal frame, then cover the frame with fabric. ZMC-2 did away with that complexity by making the aluminum skin airtight, sealing in 200,000 cubic feet of helium without need for a separate structural truss or helium vessels. As long as the structural material is light enough, this simplicity ought to decrease vehicle weight, although installing the 3.5 million fluid-tight rivets must have been a pain in the ass. Today a less laborous technique like friction-stir welding would probably be used instead.

The most fascinating part of ZMC-2's story for me is the drama that ensued when she became buoyant for the first time. Blimps and conventional zeppelins fill flexible bags that can be evacuated of air with lifting gas in order to make lift, which is a relatively straightforward process. Since ZMC-2's helium vessel was rigid, engineers needed a way to extract the nitrogen and oxygen within while replacing it with helium, all while the gases were vigorously mixing at room temperature. Since helium was and remains rare and expensive on Earth, minimizing the loss of lifting gas was critical. Replacing the ambient air within with (cheap) carbon dioxide, which mixes more slowly with helium, seemed an elegant solution at first, until, as Wikipedia puts it, "a bright young engineer" pointed out that the ship would be many tons heavier when filled with carbon dioxide, stressing the structure unacceptably. Once the necessary sections of ship were reinforced the helium purge proceeded without apparent incident, and modern engineers are left hoping we can be so clever and observant when the time arises.