The Clayton Tunnel rail crash occurred on Sunday 25 August 1861, from Brighton on the south coast of England. At the time it was the worst accident on the British railway system. A train ran into the back of another inside the tunnel, killing 23 and injuring 176 passengers. Three north-bound trains left Brighton station within a few minutes of one another. At the southern entrance to Clayton Tunnel an automatic signal failed to return to danger after the first train passed, allowing the second train to follow it into the tunnel. The signaller at the south end of the tunnel belatedly waved a red flag in an attempt to stop the second train, but thought that it had not been seen. However the driver of the second train had briefly glimpsed the flag and stopped his train inside the tunnel. The signaller then misinterpreted a 'line clear' telegraph message from the signal box at the north end of the tunnel as referring to the second train instead of the first, and signalled the third train into the tunnel. Circumstances In his cabin close to the southern entrance of the tunnel, signalman Henry Killick was in charge of a signal linked to an alarm bell, and a needle telegraph. He controlled the signal using a wheel in the cabin, and the signal would normally be at "danger" unless he set it to "clear" to allow a train to enter the tunnel. When a train had passed it, the signal was designed to return automatically to "danger", but if it did not, the alarm bell would ring. The needle telegraph was linked to a signal box at the northern entrance of the tunnel. When the signalman in the southern box pressed and held down a switch, it gave a "train in tunnel" indication to the signalman in the northern box. Otherwise, the needle on the telegraph would hang vertically. Except for the Clayton Tunnel, the line was worked on the time-interval system, which required trains on the same track to be separated by five minutes. Despite that, the three trains left Brighton within the space of seven minutes: Portsmouth Excursion left at 8.28 am Brighton Excursion left at 8.31 am Brighton to Victoria left at 8.35 am At the southern entrance of the Clayton Tunnel, the first train passed the signal at "clear", but the alarm bell rang to warn Killick