A Royal Marine from Co Antrim who built explosives for a dissident republican paramilitary group had parts delivered to his late grandmother's home, a court heard.
Ciaran Maxwell (31) stashed anti-personnel mines, mortars, ammunition and 14 pipe bombs - four of which were deployed - in purpose-built hides here and in England.
The Old Bailey heard there were 43 hiding places at eight locations.
On the second day of his sentencing hearing, prosecutor Richard Whittam QC said Maxwell, of Exminster in Devon, had ordered chemicals and other parts over the internet for delivery to Northern Ireland, and he carried ammunition with him between England and Northern Ireland by ferry.
Chemicals and materials to make more bombs, as well as an adapted PSNI pass card, a PSNI uniform and a police stab-proof vest, were found by officers in barrels and buckets buried in the ground.
Mr Whittam said: "There is evidence of purchases he made by email being sent straight to Northern Ireland.
"Delivery of some of those chemicals and equipment, they went to that address of his late grandmother's.
"There is evidence he travelled to Northern Ireland by ferry.
"It looks as though some items must have been taken by him from England to Northern Ireland. For example, the bullets.
"There is concern he might have found it easier to travel between England and Northern Ireland because of the ID he would have had."
Paul Hynes QC, defending, said the defendant lived a double life and was a "Marine by day (and) it seems republican bombmaker on leave".
"Mr Maxwell accepts he was a bombmaker and quartermaster for bomb parts," he added.
Mr Hynes told the court the serviceman had grown up as a member of a small Catholic community in Larne and had suffered bullying during his school years. "He was regularly picked on as a child by older teenagers and grown men," he said.
"That victimisation was purely as a result of being Catholic."
He was "left for dead" after an attack by a group of older men armed with hammers and clubs when he was 16 and suffered post-traumatic stress disorder, which he believes affected him throughout the rest of his life, Mr Hynes added.
Having left Northern Ireland to study archaeology at the University of Newcastle, Maxwell failed to complete his degree and returned home, where he began to drink heavily and use recreational drugs.
In 2009 he decided to try and fulfil an "ambition" to join the Marines and, shortly before a deployment to Afghanistan, met old acquaintance Niall Lehd and told him about his career.
Mr Hynes said Mr Lehd was "interested" and later revealed he had connections to those in the republican movement who thought Maxwell was "someone who might well be someone of use".
Maxwell feared for his life and the safety of his family if it became widely known he was in the British military, Mr Hynes said.
He added: "He (Maxwell) was building small devices and it became apparent that Mr Lehd was keen that their acquaintanceship should continue and become deeper and Mr Maxwell should take a part in what in the beginning was a rather unusual hobby."
Mr Hynes said Maxwell had not joined the Marines in order to gain access to bomb parts and had, by joining the elite infantry unit and becoming a signaller, joined "the wrong branch of the military".
He added: "He does not seek to specialise in the sort of activity that brings him before this court."
Maxwell, who was about to be promoted to corporal before he was discovered and discharged from the Marines, found the ammunition and detonator cables while on exercise and had not sought them out, Mr Hynes said.
And he deliberately kept the detonator devices in England rather than take them to Northern Ireland, where they could be used to make pipe bombs "ready to go".
Asked by the judge where Maxwell built the bombs, Mr Hynes replied: "Principally in Northern Ireland, mostly at his grandmother's house.
"She died in 2015, but he was able to use her address before that very occasionally for a few bits and bobs.
"Essentially when he had time to himself at his grandmother's house, that's what he did."
Mr Whittam said the serviceman, who is originally from Larne, had apparently been motivated by "a connection with dissident republicanism".
Maxwell faces years behind bars when he is sentenced, after pleading guilty in February to preparation of terrorist acts between January 2011 and August last year, possessing images of bank cards for fraud and possessing cannabis with intent to supply.
The defendant appeared in court yesterday via video-link from Woodhill prison in Milton Keynes, where he sat at a desk with a laptop, making notes and wearing a white Nike t-shirt.
Mr Whittam said his client had been attacked in 2002 and had a copy of a news report about the assault on his laptop.
He added: "This is an image recovered from a laptop at his home address.
"It's a report in the Republican News from July 11, 2002.It's headed 'Sectarianism never sleeps in Larne'.
"This defendant, aged 16, being subject to a brutal attack with, as it's reported, iron bars and golf clubs and suffering a compound fracture of his skull.
"We know of nothing that traces this offending to that attack.
"But if it's urged in mitigation that any behaviour was as a result of this attack, my Lord would have to balance that, considering if he was aggravated since 2002, did that influence his decision in joining (the Marines)?"
Maxwell was a serving Royal Marine with 40 Commando based at Norton Manor Camp in Taunton at the time of the offences.