A Royal Marine from County Antrim made 14 pipe bombs which were to be used by dissident republicans to attack police.
A court hearing to decide how long Ciarán Maxwell will serve in prison is taking place at the Old Bailey.
The court heard that four of the pipe bombs were used in Northern Ireland – and two detonated.
In February, Maxwell, 31, admitted a number of offences, including bomb-making and storing stolen military weapons.
The Larne man also pleaded guilty to drugs and fraud charges. The sentencing hearing is expected to take up to three days.
Maxwell is not in court, but is appearing via video link from Woodhill Prison in Milton Keynes.
According to the charge details, he had a stash of explosives in 12 purpose-built hides in England and Northern Ireland.
DNA evidence found at one of the County Antrim hides led to Maxwell’s arrest.
On Wednesday, the court heard that documents found on a memory card of Maxwell’s included a Mujahideen explosives handbook and the IRA’s Green Book – or rule book.
It also contained images of Larne police station marked manually with a blast radius graphic.
His wi-fi password was “tiocfaidh1” – a derivation of the Irish republican phrase “tiocfaidh ar la”, or “our day will come”.
Maxwell told police he had taken a member of the Continuity IRA to a hide where he had stashed pipe bombs in Northern Ireland.
The court was told the man he took to the hide was Niall Lehd, convicted in 2014 of possession of an explosive substance with intent to endanger life.
Maxwell had handwritten “to-do lists” mentioning “targets, dummy runs and recces” and a number of towns in Northern Ireland.
The exact details were redacted by the court, but the targets included a Territorial Army centre and substations.
There was also reference to a loyalist group, the need to notify news agencies and the words “test pipe bomb and car bomb”.
In one of his hides, Maxwell placed a modified booby-trapped torch which, when armed, would explode if turned on.
Maxwell lived in Exminster, County Devon, and was based with 40 Commando in Taunton, Somerset. He never served in Northern Ireland.
He was arrested last August and a search near Exeter found hides with a range of explosive substances, as well as ammunition, weapons and tools for making bombs.
Along with the 14 pipe bombs, the court heard Maxwell also stashed:
- Two anti-personnel directional mines
- Two explosively formed projectiles (EFPs)
- 29 complete explosive firing systems
- 33 initiators (part of a detonator for explosives), including two military initiators
- 13 military “igniter safety fuze electric” initiators
- Three fully-constructed improvised detonators
- Other component parts for IEDs [improvised explosive devices]
- Other materials and chemicals to make explosives
- A replica handgun and ammunition
On Wednesday, prosecutor Richard Whittam QC told the court: “Across 14 of the locations involved in the investigation, Mr Maxwell had in his possession, or had constructed, 14 pipe bombs… four have been deployed in Northern Ireland.
“It is our case that some of the items inevitably must have been taken from the UK to Northern Ireland by this defendant.”
He added: “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.”
The court heard dissident republicans have carried out more than 160 terrorist attacks since 2010, 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.”
The court heard that Maxwell “appeared shocked” when he was arrested.
During interview he told police he “got in over his head and didn’t know how to get away”.
After his arrest, drugs were found in locker at the camp, including herbal cannabis, cannabis resin, and hallucinogenic drugs DMT and LSD.
In March 2016, police said bomb-making parts had been found in barrels hidden in a wooded area in Carnfunnock County Park in County Antrim.
Two months later, another “terrorist hide” was found in Capanagh Forest, also near Larne.
Police described it as one of the most significant arms finds in recent years.
Of particular concern to security chiefs was the discovery of military grade anti-personnel mines.
Pipe bombs and parts for making explosive devices made up part of the haul.
Their serial numbers revealed they had been taken from the Royal Marines base in Somerset where Maxwell was based.