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“For almost 25 years, virtually every bomb constructed by the Provisional IRA and the groups that splintered off it has contained Semtex from a Libyan shipment unloaded at an Irish pier in 1986.”

-Tom Harnden, The Telegraph


Semtex is a commercially manufactured, military-grade, plastic explosive containing RDX and PETN. It was invented in the late 1950s by Stanislav Brebera, a chemist working for Synthesia, a industrial chemical manufacturer in the former Czechoslovakia.

Plastic explosives are highly versatile weapons to guerrilla fighters because of their stability and difficulty to detect. Semtex can be easily transported, stored, divided, and deployed without risk of accidental detonation by changes in temperature, pressure, moisture, or other environmental conditions. Semtex must be triggered by a detonating device so it won’t explode if exposed to open flame, intense light, electrical, magnetic or other forms of radiation. It’s waterproof. It’s very malleable, almost like putty, making it idea for hidden and improvised bombs. In addition to its stability, Semtex is far more powerful than fertilizer-based explosives, i.e., to achieve the same blast yield of a 1lb slab of Semtex might require fifty or a hundred pounds of fertilizer-based explosive packed into barrels or other large containers which would be difficult to transport or conceal, and might leak material or prematurely detonate if not handled with extreme care.

With Semtex you can shake it, bake it, bop it, pull it, twist it, pop it in your pocket and take it for a walk into a bank or police station and leave it concealed. There it will patiently wait for its primary detonator to be triggered remotely, most commonly by radio frequency transmissions which the RDX and PETN explosive material themselves are unaffected by. Most of us have seen the hero in a show scrambling to remove detonators on charges so we almost intuitively know it can be easily disarmed and even recovered for reuse, but which is not to say steps cannot be taken to prevent the detonators from being removed once the charges are planted.

In response to international agreements (resulting from the Pan Am Bombing) the manufacture of Semtex began voluntarily adding chemicals to Semtex in 1991 to aid in its detection. However, by that time tonnes of Semtex-H originally sold to Lybia was already in the hands of the Provisional Irish Republican Army.

After the tragedy of the Omagh Bombing (in which Lybian Semtex may have been used) there
was a renewed call for peace leading to the Good Friday Agreement. However, after a few years the Real IRA (a splinter organization of the PIRA which had carried out the Omagh Bombing), became dissatisfied with British commitment to the peace process and the power-sharing Northern Ireland Executive government. They began a renewed military campaign in Northern Ireland, and the English mainland. This campaign would reveal publicly that the Real IRA was still in possession of significant amounts of Semtex (originally provided to that organization by the defection of Provisional IRA quartermaster Michael McKevitt in 1997).

March 4th, 2001 [GIF/PICTURED]: Acting on a warning sent to a London hospital by Real IRA, police were attempting to disarm a car bomb outside the BBC’s main news centre when it exploded. Although Semtex was not publicly confirmed as the explosive in this bombing, a little over 1lb of unexplored Real IRA Semtex would be recovered by police after a failed improvised-rocket attack on the Strabane RUC station a couple months later in the same campaign.

After the commitment of Sinn Féin and the IRA to seek their goals through ‘exclusively peaceful means’ and the decommissioning of arms in 2005, as well as the death of Muammar Gaddafi and his regime in 2011, it seems unlikely Semtex will be used by dissidents in any future large-scale bombings. Furthermore, sympathizers in the United States and revolutionary allies such as the Basque separatist group ETA in Spain have also supplied the IRA with the slightly more effective plastic explosive C-4). Semtex also has an approximate shelf-life of 10 years, meaning old stocks are now very ripe.

However, small amounts of Semtex have been used by radical groups like Continuity IRA in
improvised devices and rocket attacks. And, as recently as September 2015 caches of up to a pound of Semtex have been discovered or seized (although the combat effectiveness of
those materials is now questionable).

-Based on exerts from The Wicklow Connection: A Timeline of Semtex Proliferation During The Troubles by Daniel O'Handley