The bomb used by the IRA at Loughgall was transported across Lough Neagh to its target by boat, it can be revealed.
The deadly device, estimated to be around 400lb, was taken from Ardboe in Co Tyrone to an isolated part of the Co Armagh shoreline near Maghery.
The device was later loaded into the bucket of the digger used in the attack.
Although the IRA had advanced their bomb making techniques by the mid-1980s, the digger bomb used at Loughgall was denoted by simple fuse wire lit using a lighter.
Republican sources say the decision to transport the bomb by boat was made to avoid the possibility of running into British army or RUC checkpoints along the maze of roads that criss-cross the border between Tyrone and Armagh.
By road, the straight route from Ardboe to the Loughgall area would have taken the bomb team through mainly nationalist districts along the lough shore until they crossed the M1 motorway and into majority unionist districts of north Armagh.
Sources say that after the bomb was loaded and final preparations were made, both the digger and bomb team made their way towards Loughgall.
It is understood the digger, which was driven by Declan Arthurs, left the rendezvous point before the other IRA members.
A hijacked blue Toyota Hiace van carrying the other bomb team members moved along the same road a short time later, catching up with the digger, which had its front bucket raised in the air, as it neared Loughgall and the RUC station.
The IRA team had planned to kill three police officers as they came off duty before blowing up the RUC station.
The digger used in the attack had been hijacked earlier from a family farm close to the main Armagh to Moy Road.
The blue Hiace van the bomb team travelled in was hijacked at Clone, near Coalisland, earlier in the day after two armed and masked men walked into business premises and demanded the keys from a staff member.
It is understood they ordered the man not to report the matter for several hours.
The hijacking was later reported to police.
However, it is believed that some members of the SAS ambush squad were aware of the stolen van before the time it was officially reported.
