Shortround6
Major General
The Hurricane was adequate for the job of intercepting bombers and contesting the fighter escort, so why change over to the Spitfire during the BoB?
1. Because the Spitfire could make some of the intercepts the Hurricane could not.
2. Because you never know when or what the enemy is going to introduce as a new weapon (not without a really good spy network)
Basing your acquisitions on "adequate" is setting yourself for a massive fail at some point down the road.
3. By the summer of 1940 (before the BoB) starts there were three (?) factories "building" Spitfires. Castle Bromwich which was months behind schedule (but unlikely to be able to be converted to make anything else without months of delay). Castle Bromwich is generally credited with with 10 ML IIs in June, 23 in July, 37 in August and 56 in Sept.
One reason for the Hurricanes continued use was the destruction of both of Supermarines main plants at Woolston and Itchen. The factories were dispersed into several dozen locations and a great job was done under very difficult circumstances The Woolston and Itchen facilities may have built 1300 or Spitfire MK Is by the time they were bombed.
total production of MK I's was almost 1600 and Castle Bromwich built very few. The dispersed facilities around south Hampton continued to build MK Is during the fall of 1940 I believe (welcome correction).
4. The British were working over time to come up the MK II Hurricane to equal the 109E-3/4 powered by DB 601 A engines. Unfortunately I have seen next to nothing comparing a 109E with the DB 601N engine (109-E4/N's and E-7s) to either Hurricane MK Is and Spitfire MK Is or te eMk II versions of either aircraft. We know the Hurricane MK II was a done deal against a 109F with the DB 601N engine. in the spring of 1941.