Vandals have caused more than £100,000 worth of damage to a new railway carriage and stolen 20 potentially lethal detonators.
Shrapnel from the detonators is capable of killing anyone in a 100ft (30m) radius and which were taken from the carriage in Coventry.
Central Trains is offering a £5,000 reward for the arrest and conviction of the offenders.
The detonators are triggered by impact and warn staff of a train accident.
The yellow disc detonators, each the size of a £2 coin, are placed on the track approaching an incident and are set off by any approaching trains rolling over them.
Security patrols
The noise of the explosions warns train drivers to stop.
The vandals also stole two fire extinguishers, 20 emergency safety hammers and broke 42 windows and glass panels in the attack last weekend.
The carriage was parked in a siding between Coventry station and a new rugby stadium at Spon End.
A spokesman for Central Trains said the depot had been attacked four times before but described this as the worst incident of vandalism.
It has now introduced security patrols at the depot in addition to CCTV in the carriage.
Police are now studying footage from the cameras to try and identify those involved.