A Royal Marine with links to dissident republicanism made 14 pipe bombs - four of which were deployed in Northern Ireland, a court heard.
Ciaran Maxwell, 31, compiled a library of terrorism documents, bought chemicals and components and went on to manufacture explosives and devices, which he stashed in purpose-built hides in England and Northern Ireland.
The 31-year-old, of Exminster in Devon, also had maps, plans and lists of potential targets for a terrorist attack - as well as images of an adapted Police Service of Northern Ireland (PSNI) pass card and a PSNI uniform.
The serviceman, who is originally from Larne in Co Antrim, pleaded guilty at the Old Bailey 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, in February.
At the beginning of a three-day sentencing hearing at the same court, prosecutor Richard Whittam QC, said: "Across 14 of the locations involved in the investigation, Mr Maxwell had in his possession, or had constructed, 14 pipe bombs."
He added: "Of those 14 pipe bombs constructed by Mr Maxwell, four have been deployed in Northern Ireland."
The court heard dissident republicans have carried out more than 160 terrorist attacks since 2010, involving tactics including the deployment of improvised explosive devices (IEDs) such as pipe bombs.
Mr Whittam said: "Whilst attacks are mainly directed at members of the police, military and prison service, the nature of the attacks leaves members of the public at risk.
"All of the groups remain persistent in their intention to kill and seriously injure."
The court heard Maxwell was a serving Royal Marine Commando at the time of the offences, having enlisted on September 27 2010.
He joined 40 Commando at Norton Manor Camp in Taunton the following year as a rifleman, undertaking some duties in the United States.
Maxwell, who has been discharged from the Marines, was also deployed in the UK - but never in Northern Ireland, said Mr Whittam.
"Between 1 January 2011 and 24 August 2016, Mr Maxwell researched the manufacture and construction of explosives, acquired the items he needed to make explosive devices and constructed the devices," he said.
"He stored the items he needed to make the devices, the devices themselves, ammunition, weapons, tools and resources in hides across England and Northern Ireland.
"He engaged in research to create of a library of maps, plans and lists of potential targets for a terrorist attack."
Along with the 14 pipe bombs, Maxwell also stashed two anti-personnel directional mines, two explosively formed projectiles (EFPs), 29 complete firing systems, 33 initiators - including two military initiators, 13 military "Igniter Safety Fuze Electric" initiators, three fully constructed improvised detonators and other components parts for IEDs.
The court heard he had hoarded more materials and chemicals to make explosives, as well as a replica handgun and ammunition.
The court heard it has been "commonplace" for Northern Ireland-based terrorist groups to conceal bomb-making equipment and other terrorist material in purpose-built hides.
But Mr Whittam said: "In recent history and certainly over the last five years, the number of hides in this case, their geographical dispersal, their attribution to a single person constructing and managing them and the amount of material stored within them, would be highly unusual."
The prosecutor described how a walker stumbled on one of Maxwell's in Carnfunnock Country Park, near Larne, in March last year.
Another was found in Capanagh Forest in Co Antrim in May by someone searching for a suitable place to camp, the court heard.
The court heard that ammunition used by the British Armed Forces was found along with bomb-making materials and IEDs.
Mr Whittam said: "It is our case that some of the items inevitably must have been taken from the UK to Northern Ireland by this defendant and it may be that, when travelling between England and the UK, bearing in mind the identity cards he would have had and his position, his passage would have been easier than others to take items with him."
Maxwell appeared in court by video link from Woodhill prison in Milton Keynes, where he sat at a desk with a laptop and making notes.
The court heard he was being watched by police by the middle of August last year and was repeatedly seen going to and from Powderham New Plantation, near Teignbridge, Devon.
The court heard he looked "shocked" when he was arrested on suspicion of terror offences at his base in Taunton, Somerset on August 24.
From a search of his work locker, officers seized cannabis and hallucinogenic drugs DMT and LSD, while items including hand-written notes were recovered from his Exminster home.
On one, headed "Easter Leave", was written "test pipe bomb" and "recce (of a town in Northern Ireland redacted in court)".
The court heard similar "to do lists" were found in one of 13 hides initially found by police in the Powderham woods.
"Some things obtained, to get, some things to be tested," the prosecutor explained.
From September 2 Maxwell provided police with "extensive information" about further hides and items in Powderham, including a modified torch, which was designed to act as a booby trap, exploding in the hand of anyone who tried to turn it on.
He also told officers about more hides in Northern Ireland, including at the Old Bleach Works in Larne, where he said he had been with his friend Niall Lehd, who told Maxwell he was part of the Continuity IRA.
Among the items found were five pipe bombs and DDNP – a high explosive seen in Northern Ireland for only the second time.
The first example was recovered following an explosion in Larne, after which Lehd was jailed after pleading guilty to possessing an explosive substance with intent to endanger life in 2014.
The court heard the February 2013 blast was one of four pipe bomb "deployments" linked to Maxwell.
A detonated pipe bomb was recovered following an explosion in December last year, while another undetonated device was found against a windowsill of a house in Carnlough.
Components of a fourth pipe bomb were found in Belfast.