11 April 1942. Glasgow, Scotland
North British Locomotive’s work on the order for 240 Tetrarch Light Tank Mark VII was continuing at its relatively slow rate, but nearing completion. The majority of those built in the last year were fitted for the Duplex Drive system for amphibious use. The rest were destined for use by the glider equipped airborne forces. While orders for the follow-on Mark VIII Light Tank hadn’t been forthcoming, a team from Vickers had arrived with the drawings for the follow-on vehicle, a self-propelled gun based on the Tetrarch’s hull, known as SP3 by Vickers.
Leslie Little’s idea, with Sir John Carden’s help, had filled a roll that the airborne units needed, but that the limitations of the Tetrarch couldn’t fully meet. The idea of a tank that could be delivered by a glider to act in various roles such as reconnaissance vehicle/anti-tank/Close Support had looked at two options. The British Tetrarch or the American T9 proposal from Marmon-Herrington both suffered from limitations.
The success of the American M3 Light Tank, the Stuart, had shown that there was still a place for Light Tanks, and with amphibious and airborne needs growing, the War Office was looking for the right fit. The initial design for the Mark VIII, with its heavier armour but with the same engine as the Tetrarch, had failed almost at the first hurdle.
Removing the turret from the Tetrarch, allowed Vickers’ designers to fit either the 6-pdr anti-tank gun, or the new 95mm Close Support gun into a built-up Tetrarch hull. The weight of the Self-Propelled Gun (SPG) was low enough to be viable for the glider idea, and it would give the airborne troops a very low silhouette vehicle, with the capacity to act either in the anti-tank role or the close support role. Like all SPGs, it’s gun would have a limited traverse, but the designers believed that the steering system of the Tetrarch would make it capable enough. It was even suggested that the vehicle could be used to tow artillery pieces should that be needed.
Because it used the same components of the Tetrarch, North British Locomotives would have no problem switching from one to the other. One of the Tetrarch’s had been taken to Chertsey, where the Vickers team had made the necessary changes. Fitted with the 6-pdr gun, also fitted to the Valiant Mk II, it had been taken to Farnborough for testing, and then Lulworth for gun testing. The reports from both trials had been complimentary but the problem seemed to be that it fell between two stools.
Anti-tank guns were the provenance of the Royal Artillery, who weren’t terribly keen on the Self-propelled gun concept. The Royal Armoured Corps were less worried, but it was too lightly armoured to really be considered a tank, and as a tracked vehicle it wasn’t an armoured car. Major-General Browning (GOC 1st Airborne Division) had been present at the demonstration and excited at the capability the self-propelled gun. He had been trying to develop the idea of the Parachute force into a proper Division, with all the support functions necessary to do the job an airborne force would need to complete its mission. Artillery and anti-tank guns were high on his list of priorities. The problem for light forces, like paratroopers, having guns also meant they needed a vehicle to tow the guns, and carry ammunition. Space and weight on gliders was going to be limited, so having a light vehicle that carried its own gun and ammunition would be a godsend. The SP3 was about the same weight as two universal carriers, was slightly better protected. The fact that it could carry either the 95mm or the 6-pdr made it doubly useful. Browning asked if it might also be able to carry a 25-pdr gun, which had caused a bit of a panic among the Vickers people, and indeed the War Office officials.
The prototype glider, designed for and capable of carrying a Tetrarch, had flown successfully in March. The Tetrarch was always going to be limited with the 2-pdr gun, even the 3-inch close support gun. An SP3, with the either the 6-pdr or 95mm, would give the paratroopers an edge that they could very well need. ‘Boy’ Browning became an enthusiastic supporter of providing the 1st Airborne Division with the kind of light armoured vehicles that would provide his men with the support they’d need.
