The initial contract for Supermarine was for 310 dated 3 June 1936. The first Hurricane order was also in 1936 and was for only 600 aircraft. That was way back at the start of the rearmament programmes when war, if it happened at all, still seemed to be in the distant future.
And with the pace of aircraft development being what it was in the 1930s, how many do you order in 1936.The Spec for a successor to the Hurricane & Spitfire, F.18/37 to meet a requirement for a 400+mph fighter was issued in March 1938, just 5 months before the Spitfire first entered service with 19 squadron. While the competition was won by Hawker, who had already been working on a successor for some time that lead eventually to the Typhoon, submissions were also made by Supermarine, Gloster, Fairey & Bristol.
In 1936 war seemed a long way off. Planners in many nations were looking to 1942 or even 1944. It was only in summer of 1938 with the Munich crisis, that war suddenly seemed much closer.