In the 1860s, London built a futuristic underground network that few people remember today. Long before the Tube or Mail Rail, the Pneumatic Despatch Company operated a series of capsule trains—powered by compressed air—that shuttled letters and parcels beneath the city at breakneck speed. It was efficient, innovative, and ahead of its time. Backed by major investors and the British Post Office, this Victorian system promised to solve the city’s growing logistical challenges. At its peak, it could send mail between stations in under a minute. But just over a decade later, it vanished—abandoned, sealed off, and largely forgotten. So what happened to the Pneumatic Despatch Company? And could parts of it still survive beneath modern London?