Not wanting another 'all singing, all dancing RAF' this time, rather take an idea from another forum - just a host of improvements made in 1939 to mid 1940 that might snowball in a more capable RAF for the BoB, and, if possible, BoF. Improvements can range from organization, tactics, whole aircraft and aircraft-related items. The 'cut-off' date (or, date to start with improvements) is March 15th 1939 - date the German army entered Czechia.