Northumbrian Revival

In the anxious summer of 1940, when the threat of German invasion hung heavily over Britain, a remarkable variety of improvised defensive vehicles appeared across the country. Among the most unusual of these was the Thornycroft Bison mobile bunker. At first glance it looked less like a vehicle and more like a small concrete pillbox mounted on a truck chassis. Its strange appearance reflected the desperate and innovative atmosphere of the time, when Britain was preparing for the possibility of invasion with whatever materials and vehicles could be found.

The Bison was essentially a mobile fortified position. Its design was simple in concept but formidable in appearance. A thick concrete structure was mounted onto the chassis of an old civilian truck, turning the vehicle into a heavily protected firing position that could be moved where it was needed. The concrete structure was built with loopholes positioned around its sides so that the men inside could fire their personal weapons outward. These openings allowed defenders to cover the surrounding area in every direction, creating a defensive coverage of nearly 360 degrees. The only areas that could not be directly covered by the loopholes were those blocked by the cab’s structure, although the vision slits in the cab itself could be used to observe and fire into these blind spots if necessary.

Inside the bunker, the arrangement of the crew was never strictly standardized. Unlike most military vehicles, the Bison was not designed with a fixed crew size or official layout. The number of men operating one of these vehicles, where they positioned themselves during combat, and what weapons they carried were largely determined by the unit using it. Different Home Guard units or military formations adapted their vehicles according to their own needs and local circumstances. What remained consistent was the limitation imposed by the firing ports. These loopholes were only suitable for personal firearms such as rifles or submachine guns. Larger mounted weapons, machine guns on tripods, or other crew-served weapons could not be used through the openings.

Access to the interior of the bunker was somewhat unusual. The crew typically entered through an opening cut into the base of the flatbed beneath the concrete structure. Once inside the protected space, they could move forward and reportedly climb into the driver’s cab through an opening in the roof. This arrangement allowed the crew to remain under cover while entering the vehicle and moving between the driving compartment and the bunker itself.

One of the most interesting aspects of the Bison concept was its flexibility. The design could be fitted onto almost any suitable truck chassis. Because of this, Bisons appeared on a wide variety of vehicles with different engines, wheel configurations, and drive systems. Despite these differences, the vehicles all shared certain characteristics. They were almost always built on civilian trucks that were no longer considered particularly useful for normal wartime service. Many of these vehicles were already old by the standards of the early 1940s. Some dated back to the First World War, while others were even earlier designs.

The use of these aging vehicles was practical. Britain could not afford to divert modern military trucks for such experimental defensive projects, but there were many obsolete commercial vehicles available that could still carry heavy loads at slow speeds. These were ideal candidates for conversion. In one especially curious example, a steam-powered truck was converted into a Bison. In this case the steam engine and all its associated equipment were removed before construction began, and the remaining chassis was turned into a trailer carrying the concrete bunker.

The question of how these trucks were obtained remains somewhat unclear. During the war the Home Guard frequently used privately owned vehicles that had been loaned or informally requisitioned by local units. Those arrangements were usually temporary and based on agreements between vehicle owners and the local Home Guard commanders. The Bison program appears to have been different. It was an official government effort intended for use by the armed forces rather than a local improvisation. This suggests that the trucks were likely purchased, formally requisitioned, or otherwise obtained through official channels, with compensation offered to their owners.

Evidence supporting this idea comes from the limited historical records of at least one known Bison vehicle. In that case, the original owners never attempted to reclaim the truck even after it had been abandoned. This strongly suggests that ownership had already been transferred to the government and that some form of payment or compensation had been arranged.

The construction process for the Bison was both simple and ingenious. Although each vehicle differed slightly in shape, especially around the cab and bonnet, the basic building method was the same. Once a suitable donor truck arrived at the Concrete Ltd works, workers began by stripping away any unnecessary bodywork and excess weight from the chassis. This preparation ensured that the vehicle could carry the enormous mass of the concrete structure that would soon be added.

After the chassis had been prepared, wooden shuttering was built around the cab and bonnet to form the shape of the protective concrete shell. Inside this framework, several layers of expanded metal mesh were placed. This metal reinforcement helped strengthen the concrete once it hardened, preventing it from cracking under stress. Concrete was then poured into the shuttering, gradually forming a thick protective armor around the front of the vehicle.

The bunker itself was built separately as a precast structure. Constructed using the same reinforced concrete technique, it formed a solid rectangular fighting compartment designed to sit on the flatbed of the truck. Once completed, this heavy structure was lifted into position and secured to the chassis. Finally, a precast roof was attached to complete the bunker and seal the crew inside their fortified shelter.

The resulting vehicle was extremely heavy and slow, but speed was never its primary purpose. The Bison was intended to act as a movable strongpoint rather than a fast combat vehicle. It could be positioned at roadblocks, defensive lines, or key approaches where its thick concrete protection would shield the crew from small-arms fire and fragments while they returned fire from within their mobile pillbox.

Despite its striking appearance and the ingenuity behind its design, the exact number of Bisons produced remains uncertain. Surviving records are incomplete, and many of the vehicles were dismantled or scrapped after the invasion threat passed. Most historians believe that roughly two hundred were built, although this figure is based on secondary sources rather than definitive documentation.