Airship

Some time after the fall of the Master, the Brotherhood of Steel constructed airships (zeppelins) and dispatched them to the east, to locate and assess to the extent of the remaining super mutant threat. However, a great storm broke and blew the main airship far off course.

The ship suffered severe damage, with smaller sections torn loose from the main craft, never to be seen again. The damage caused by the storm also claimed many of the Air Convoy leaders, including Paladin Latham.

The command zeppelin remained aloft, thanks to the efforts of the surviving crew, who managed to keep the wounded vessel airborne until it reached the outskirts of Chicago. There the ship crashed and those who had lasted through both storm and the crash-landing eventually formed the Midwestern Brotherhood of Steel, a new organization, which diverged greatly from the ideals of the old Brotherhood.

One of the wrecked zeppelins can be found near the area later known as Osceolla. It was there that Paladin Latham, having somehow survived his ejection from the airship, established his main base after taking the name of Gammorin and becoming leader of the super mutants to be found there.

By the time of Fallout 4, the Brotherhood of Steel makes use of airship technology in the Commonwealth.
 * When talking to Kells he can be asked about other airships.

Appearances
A destroyed airship is seen and visited in Fallout Tactics, while a fully working one, the Prydwen, is in Fallout 4. The Prydwen was constructed by the East Coast Brotherhood of Steel over a 6 year period. It took two years to collect the materials necessary and another four to actually construct the airship. It weighs in at forty thousand tons. The fuel source was taken from a wrecked aircraft carrier's nuclear reactor. The airship is also filled with hydrogen.