'XD' was a British series of planned demolition operations to prevent the capture of oil installations and stocks by the Germans (1940).

The unit responsible for these undertakings was the Kent Fortress Royal Engineers, which was a British territorial unit, and this first became notable through its successful actions of May 1940, when it destroyed substantial oil stocks and installations just ahead of the German advance into North-West Europe.

The unit had been formed in 1932 to provide coastal defence as an alternative to regular troops, which could therefore be used elsewhere. It was a company-sized unit recruited almost entirely from the staff of the Blue Circle Cement Company. Under its first commanding officer, Major (later Brigadier) Clifford Brazier, the KFRE was soon recognised as a notably efficient unit.

In May 1940 the Germans invaded the Netherlands, Belgium and France. The British military authorities were determined that the large oil installations at the major ports in the Netherlands and Belgium should not fall into German hands and thereby ease the overextended German fuel supply situation. The implementation of these 'XD' operations was allocated to the KFRE, which was despatched in secrecy on 11 May to Amsterdam to negotiate with the local commanders and destroy the installations and the large oil stocks, which it achieved before assisting with dockyard demolitions. The unit’s success came despite the lack of advance planning and specialised equipment.

After Amsterdam, KFRE detachments carried out more oil demolitions at Rotterdam and Antwerp, and assisted with the evacuation of 40 tons of Dutch gold from Rotterdam. At times, fire was exchanged with German advance patrols.

As the German advance continued into France, the KFRE was sent to destroy the oil depots along the lower reaches of the Seine river. Initial, but understandable, French reluctance to these activities was overcome as the Germans reached the area, and the installations at Rouen, Le Havre and Honfleur were all destroyed. In addition, a large British military fuel dump near St Nazaire was destroyed. A refinery at Donges was reprieved when a British general ordered that no demolition was to be done, and the supplies were subsequently thought to have been used to fuel U-boats.

As an afterthought, detachments were sent to destroy smaller depots at Dunkirk, Boulogne and Calais. These efforts were abortive, however, for the facilities at Dunkirk were destroyed by German bombing, those at Calais were unapproachable as a result of the heavy fighting, and those thought to be located at Boulogne did not in fact exist. Further oil demolition operations were attempted at Caen, Cherbourg and St Malo, but only that at the last was successful. The Germans had taken the installations near Caen before the British arrived, and the French authorities prevented demolition at Cherbourg where, instead, the KFRE assisted in the demolition of the harbour installations.

Although these actions remained secret at the time, there was official appreciation.

During the British evacuation from western France in 'Ariel', the final KFRE detachment on the European continent lost seven men on Lancastria when this vessel was sunk at St Nazaire. One more became 'missing, presumed dead' during the destruction of the British dump near St Nazaire and another died of wounds sustained at Boulogne.

There were later grave worries that the Germans might attempt to capture the large British-owned oilfield at Kirkuk in northern Iraq. Although apparently far removed from any war zone, the region had a strong attraction to the Germans, whose had fostered and indeed continued to support pro-Nazi factions in Iraqi politics. German aircraft had reached Baghdad via Vichy Syria in the Anglo-Iraqi War of April/May 1941, and some German special forces had been planning to establish bases in the Kirkuk area, using aircraft provided by a dedicated special forces air unit. An officer of the KFRE was therefore despatched to Kirkuk with some urgency to review the situation. Apart from three wells needed to supply the Eastern Fleet, all the wells were filled with concrete and drilling rigs were removed. Local management had already made adequate plans to render the pipelines useless to the Germans.

During the latter half of 1940, the KFRE had been joined by other Royal Engineer units of the Territorial army to create the Corps Troop Engineers. After helping the construction of coastal defences against the anticipated German invasion, and clearing up and making safe bomb damage in London, the new unit was moved to a camp near Portadown in Northern Ireland as III Corps Troop Engineers.

The northern Norwegian island of Spitsbergen was inhabited by Soviet and Norwegian miners who exploited the rich coal seams there. A KFRE detachment was part of 'Gauntlet' to destroy the coal mines and stockpiles and deny their use to the Germans.

A party of nine officers and NCOs spent four months at Gibraltar, training local engineers in the destruction of oil storage facilities should this became necessary in the event of a German attempt to capture Gibraltar.

In response to the possibility of an Axis invasion of Greece, at the end of 1940 a KFRE company was sent to Greece to assist with preparations for Allied troops, train Greek army officers in demolition techniques and carry out demolitions. The KFRE party was then transferred to Thessaloníki and Volos and, as the Germans approached in 'Marita', demolished installations such as oil refineries, engineering works, gas works, port facilities and, at Volos, the fortifications. Outside Athens, a new airfield and its equipment were destroyed. Some members of the engineer detachment were lost, as casualties or captured, before the survivors were evacuated to Crete in 'Demon', where most of the others were captured or killed when the Germans invaded and took the island in 'Merkur'. Those who escaped Crete were then based in Palestine.

A detachment was employed during the 'Exporter' invasion of Vichy Syria in July 1941: during this operation a two-man team were flown behind Vichy French lines to destroy a vital bridge, and was then recovered by air. Once absorbed into the local military organisation, the engineers assisted with the wide variety of tasks performed by the Royal Engineers: construction and destruction, booby trap and mine clearance (often under fire), water supply, construction of dummy installations to deceive the enemy, etc.

The newly formed British airborne force required sapper support and in early 1942, No. 2 Company in Northern Ireland was selected for conversion to this role.