Picture a 777-foot flying machine with two promenade decks, gold-trimmed dining rooms, and an asbestos-lined smoking room suspended beneath millions of cubic feet of flammable hydrogen. This was the R101, the largest aircraft in the world, brought down not by a bomb but by a crawling 13-mile-per-hour crash.

This episode is a master class in what happens when untested engineering meets impossible political deadlines. We trace how Britain's imperial airship dream became a monument to hubris, and why this slow-motion tragedy killed 48 people and ended British airship development forever.

• Fear of fire after the 1921 R38 disaster drove the choice of heavy diesel engines, triggering a domino effect of fatal design compromises.
• The ship used heavy stainless steel joints and 4,700-pound Beardmore Tornado engines originally built  ...