British Transport Police (BTP) is appealing for witnesses after three trains were damaged at a bridge near Shotton Low Level station, Deeside.
BTP and train operator Arriva Trains Wales have released photographs of the damage caused to two of the trains which they said could have resulted in serious injury - or worse - to the drivers involved.
The first incident happened at about 8.35pm on Saturday 13 June when a train travelling from Llandudno to Manchester Piccadilly is believed to have struck an object deliberately suspended from a bridge one and a quarter miles on the Flint side of the station.
The second train, travelling from Holyhead to Crewe, was damaged in a similar way about one and a half hours later.
The third train, travelling from Crewe to Holyhead was damaged at about 1.25pm the following day, Sunday 14 June, after an object, believed to have been a brick or stone was thrown at the train.
In all three cases, the driver's cab window was smashed and the trains had to be taken out of service for repair.
Although none of the drivers was injured, all were badly shaken by the incidents, which BTP is treating as extremely serious.
A BTP spokesman said:
"At this stage it appears that these were three very serious acts of vandalism and it was fortunate that the train drivers were not injured.
"We have collected a significant amount of forensic evidence at the scene and are currently examining these items, as well as following other lines of enquiry.
"Officers have also been conducting plain clothes and high-visibility patrols in the area.
"Given the serious nature of these incidents, and the fact that the train drivers could have suffered serious injuries, or worse, it is vital that anyone with information contacts us immediately.
"Whoever did this put people's lives at risk."
Arriva Trains Wales security manager, Gwilym Bowen said:
"These are foolish, dangerous acts of deliberate vandalism and it is fortunate that there was no loss of life or serious injury although our train crew were severely shaken by the incident.
"Three of Arriva Trains Wales trains had to be taken out of service for repair and as a result these idiots caused delays and cancellations to our passengers.
"We will be working closely with British Transport Police as they gather the forensic evidence which we hope will lead to arrests."
Anyone with information is asked to contact BTP on Freefone 0800 40 50 40.
Alternatively call Crimestoppers, anonymously, on 0800 555 111.
Police Force: British Transport Police (BTP)
Address:
Low Level station
Shotton
FLINTSHIRE
CH5
The location of the incident marked on this map is approximate