The 17 pdr anti-tank gun was approved for service in May 1942 and it was decided that it need to be mounted on a self propelled tank chassis. It couldn't be mounted any any tanks available at the time as it was too big. Initially it was thought to used the Bishop, but this was impracticle. Then the Crusader tank was chosen but it was unreliable. Vickers was then asked to use a Valentine chassis. The Valentine was in production and could be easily modified.
The gun was mounted with it facing towards the rear as it was too long and heavy to face forwards. It was found that using the Archer in an ambush position was the preferred method of use. The Archer had a low silhouette which helped in concealing it in battle.
The driver was located in the front of the Archer, but he couldn't remain in his seat when the gun was fired. The breech was directly behind his head.
Tank Destroyer Armament Performance