David Slater
That August morning in 1861 began like so many others on the London–Brighton line: express trains threading their way into the mouth of Clayton Tunnel, controlled by a pair of semaphore arms and the telegraph wires linking two signal cabins. Shortly after 8:30 am, Signalman Killick in the southern box levered his home signal to clear and admitted the approaching train.
Seconds later, the automatic treadle—hidden beneath the sleepers—jammed. Almost at once, an alarm bell clanged in the cabin, announcing that the signal had not returned to danger.
Barely three minutes after the first service entered—well short of the five‐minute timetable interval—the whistle of the second express pierced the morning air. Alerted by an alarm, Killick recognized the failure: the mechanical backstop he trusted had betrayed him. He sprinted from the box, red flag in hand, and dashed onto the ballast beside the tunnel mouth, in time to see the second train speeding past. The driver caught that frantic flag warning, braked hard, and ground to a halt deep within the tunnel, his wheels skidding to a standstill on the rails. Obedient to the emergency halt, he then reversed the train slowly toward the portal to comply with the flagged stop signal and find out why.
Back in the box, Killick’s telegraph needle flickered with a “Train Out” indication. Believing this belatedly to refer to the halted second express, he realised that the home signal at Clear was appropriate in its failed state, and he would not need to signal stop. Thus, the third express thundered in at full speed. Deep in the darkness, the reversing train and the on-rushing locomotive met in a violent collision. In minutes, the wreckage would claim twenty-three lives and maim nearly a hundred and eighty more.
That day, the alarm bell—intended as the fallback for a failed treadle—proved too late to prevent catastrophe. A single device’s malfunction, a compressed timetable, and a mis‐read telegraph message had resonated into tragedy, teaching the railway world that no one safeguard, however loud its warning, could be allowed to stand alone.