#Standard Improvised Munitions

The PIRA Mark 12 mortar was first used on 26 October 1989 to attack a Security Force observation post in Crossmaglen
using a multiple launch tube assembly. During the attack it was used in combination with the Mark 11 mortar, two of
which were intended to tear a hole the outer steel mesh to allow two Mark 12s to explode directly against the base wall.
Although categorized as a mortar for reporting purposes, it can more accurately be described as an improvised
Off-Route HEAT (High Explosive Anti-Tank) projectile and is most commonly used in a direct-fire role to attack passing
army and RUC patrol vehicles.

The Mark 12 is similar in general appearance to a military mortar round and is made of folded and welded steel sheet.
It is fired from a launch tube consisting of a cut down steel gas cylinder and was most likely manufactured in the South
and issued to an Active Service Unit as complete assembly and ready for use. The warhead contains a backwards
facing mild steel cone located in the front to create an armour piercing hollow-charge effect. The warhead contains a
payload of around 5lb of SEMTEX-H high explosive and is designed to explode on impact using a heavy inertia pellet
housed in the tail section and a .22 rimfire blank. The inertia pellet is in the form of a heavy steel bar with one end
ground to a chisel-point and secured in a short section of tubing via two lengths of thin copper wire. Upon impact the
copper wires shear, allowing the striker bar to move forward and crush a light creep spring, striking the .22 rimfire blank
which flashes through to a plain detonator. The propulsion unit is separate and consists of a perforated steel pipe and
coupling welded to a pusher plate of a similar diameter to the inside diameter of the launch tube. A 200 gram charge of
homemade black powder is contained within the pipe which is initiated by a flash bulb igniter. The pipe is wrapped in
electrical tape to seal it and ensure reliable combustion of the propelling charge inside. The Mark 12 uses the same
rolled steel gas cylinder tubing for its launch tubes as the Mark 10 mortar bomb.

The Mark 12 proved to be a particularly versatile weapon, and the IRA became adept at concealing it in carefully selected
ambush positions. In March 1992 a single Mark 12 was fired from a parked car at a passing Army patrol vehicle from a
distance of 2 meters scoring a direct hit. The projectile was launched from a hole cut in the boot lid which had been
camouflaged using using spray-painted cardboard. The attacker was positioned on the opposite side of the Newry
Canal and used a photographer’s flashgun and ‘photo slave’ flash initiation system to trigger the device from a safe
distance. A permanent feature at the side of the road such as a tree, street lamp or telephone pole was often used as a
reference to position the device which would be fired just as a vehicle appeared in-line with the object.

Highly accurate EOD reference model + diagrams and photos.