The 17 pounder anti-tank gun was a very powerful gun but also very large, heavy, and could only be moved about the battlefield by a vehicle, which made the gun more effective in defence than in the attack. A version of the Churchill tank had been tested as a self-propelled gun; the "3-inch Gun Carrier" and the US was expected to be able to provide the M10 Wolverine through Lend-lease. Other projects were considered using obsolete tank chassis. Possible vehicles included the Valentine, for its reliability and low profile, and the Crusader, for its good power-to-weight ratio. In development were tank designs using the 17-pdr, which led to the Cruiser Mark VIII Challenger tank (and its post-war variant the Avenger), derived from the Cromwell cruiser tank, and the Sherman Firefly conversion of the Sherman tank.
The Valentine chassis was soon chosen, as it was in production but obsolescent as a tank in British use, and was also one of the few chassis that could accommodate such a large gun. The engine in the Archer had a higher power rating than in the Valentine. Since the Valentine had a small hull and it was not possible to use a turret, the gun was mounted in a simple, low, open-topped armoured box, very much like the early Panzerjäger German self-propelled guns in appearance, with the gun facing to the rear, which kept the length of the Archer short. The mounting allowed for 11 degrees of traverse to either side, with elevation from -7.5 to +15 degrees.
On firing, the gun breech recoiled into the driver's space, with the driver staying in position, in case the vehicle needed to move quickly. The rear mounting combined with its low silhouette made the Archer an excellent ambush weapon, allowing its crew to fire, then drive away without turning round.
The first prototype was completed in 1943, with firing trials carried out in April 1943. Vickers were given orders for 800 vehicles.