During the height of Northern Ireland’s “Troubles” in the 1970s and ‘80s, the British government incarcerated hundreds of Provisional Irish Republican Army (IRA) paramilitaries inside the notorious Maze Prison. Touted as Europe’s most secure penitentiary, the Maze was thought to be escape-proof—that is, until 38 IRA prisoners staged the biggest jailbreak in British history in September 1983.

Built on a former Royal Air Force Base 10 miles outside Northern Ireland’s capital of Belfast, the maximum-security prison featured eight jail blocks shaped like the capital letter H. These H-Blocks became battlegrounds for IRA prisoners who had waged a violent campaign to end British rule in Northern Ireland. After the British government stripped convicted paramilitaries of their special status as political prisoners in 1976, IRA inmates wore blankets instead of prison-issued uniforms and refused to shower or empty their chamber pots. The protest culminated in a 1981 hunger strike in which 10 republican prisoners—including the IRA’s leader in the Maze Prison, Bobby Sands—died.

IRA inmates, who were serving time for crimes ranging from murder to the possession of explosives, viewed the Maze as a prisoner of war camp. Believing it their duty to attempt an escape, IRA leaders held inside H-Block 7 spent four months during the summer of 1983 hatching an audacious jailbreak.

READ MORE: How the 'Troubles' Began in Northern Ireland

The prisoners initially engaged in a charm offensive to build a camaraderie with prison officers, getting to know them on a first-name basis and harvesting information. High-ranking IRA leaders serving as janitorial orderlies used that camaraderie to gain greater access around the jail, even being permitted to perform cleaning duties inside “the circle,” the nerve center located in the middle of the H-block.

Knowing that officers only carried batons for self-defense, the inmates smuggled six handguns with silencers and knives inside the prison, although it’s still not known how. After taking control of the H-block at gunpoint, the prisoners planned to hijack a food delivery truck, which they learned was not searched when entering or exiting the prison. Having decided to stage the breakout on a Sunday—the quietest day of the week with the fewest staff on duty—the IRA leaders set September 25, 1983, as the day for their great escape.

READ MORE: Irish Republican Army: Timeline

That afternoon, five IRA prisoners entered the circle of H-Block 7 to carry out their cleaning duties. Everything appeared routine until shortly after 2:30 p.m., when Brendan McFarlane—who had succeeded Sands as the commanding IRA officer inside the Maze—called out “Bumper!” Hearing the pre-arranged codeword, the inmate-orderlies flashed their guns and overpowered the unarmed prison guards.

Since officers regularly kept the solid bulletproof door to the control room open for ventilation purposes due to a prison design flaw, an inmate identified by guards as Gerry Kelly was able to point his gun through a grill gate at officer John Adams. Kelly ordered Adams to step away from the room’s radio, alarm and telephone systems and lie on the ground with his hands behind his head. “I have nothing to lose; you know what I’m in for,” said Kelly, who was serving two life sentences in connection with a deadly IRA bombing in London.

When a guard unexpectedly walked out of a nearby restroom and distracted the prisoners, Adams attempted to raise the alarm. According to Adams, Kelly then fired two shots, the second of which struck him above his left eye but proved not to be fatal. (Kelly has never admitted to pulling the trigger.)

As the five orderlies secured the circle, lookouts in a direct line of sight entered each of the block’s four wings and attacked guards with weapons that included a gun, knife, screwdriver and hammer. Within minutes, the IRA took complete control of H-Block 7 from the 24 officers on duty.

After confining prison officials to a pair of game rooms, the inmates ordered a dozen of them to remove their uniforms, which they then donned. The IRA members then bound the guards, placed pillowcases over their heads and issued a warning: “This is an IRA operation. We’re not here from revenge or to punish you over the hunger strikes, but if you interfere with the escape, you will be dealt with swiftly.”

WATCH: Full episodes of Great Escapes with Morgan Freeman online now.

The prisoners hijacked the food delivery truck when it arrived at 3:25 p.m., but their getaway was delayed as IRA intelligence officers spent valuable minutes rummaging through prison files in search of details about informers while also removing any photographs and documents that could aid in their own recapture. At 3:50 p.m., 37 prisoners piled into the back of the food truck, while Kelly laid in the passenger side footwell with a gun directed at the officer driving the van to ensure his compliance while driving to the main gate, the last obstacle to freedom.

At the gate, nine of the prisoners disguised as guards stormed the lodge where officers checked in and out and seized them at gunpoint. The delay in leaving the H-block, however, meant that guards were beginning to arrive for their next shifts. As their numbers grew, the officers fought back against the inmates.

Amid the melee, prison officer James Ferris bolted from the lodge and shouted to the guard at the pedestrian gate to sound the alarm. A prisoner, identified by guards as Dermot Finucane, gave chase and stabbed Ferris three times in the chest. The officer collapsed and later died from a heart attack. The prisoner, meanwhile, continued to the pedestrian gate, where he stabbed two officers arriving for their shifts as well as the officer on gate duty before he could sound the alarm.

When quick-thinking guards wedged their cars between the prison gates to block the food truck’s path, the inmates opened the vehicle’s rear door and fled on foot, scaling the exterior fence to freedom.

READ MORE: 8 Remarkable Prison Breaks

While some escapees hijacked cars, others fled on foot into the countryside. A massive manhunt by police and the military resulted in the recapture of 19 prisoners in the first 24 hours after the jailbreak. Most of the fugitives returned to their original cells inside H-Block 7 after their brief flicker of freedom.

Those who remained on the lam hid inside barns and safe houses before the IRA facilitated their passage to the Republic of Ireland. Several continued on to the United States under new identities, while others resumed their paramilitary activities. Three of the fugitives subsequently died in IRA operations, while Kelly and McFarlane were arrested in Holland in 1986 and returned to the Maze along with several other escapees extradited from Ireland and the United States.

The Maze Prison break boosted the IRA’s morale, but it left prison officers with lasting physical and mental scars. In addition to the death of Ferris, shooting of Adams and non-fatal stabbing of three other guards, 13 officers were beaten and 42 subsequently suffered from nervous disorders. Following the early release of hundreds of inmates as part of the 1998 Good Friday Agreement, the Maze Prison closed in 2000. The H-Blocks were demolished in 2006.