The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

310 fighters had been built, and 338 bombers. That might also sound like a
large number but it soon wouldn’t be if the Luftwaffe continued to sustain
losses at even a fraction of the rate suffered on that first day.
Although there had been sporadic small-scale aerial engagements over the
previous autumn, winter and spring, and although the RAF and Luftwaffe
had faced each other in an unequal contest in Norway, it was 10 May that
really marked the beginning of the aerial clash between Britain and
Germany – a clash that would continue all through that long summer and
autumn of 1940, and would have far-reaching and decisive consequences
for the rest of the Second World War. In terms of barefaced courage, that
opening salvo showed that the two sides were evenly matched. But courage
would not be enough for the men of the RAF or the Luftwaffe. What they
both needed were planes – good planes suitable for the task given them –
aircrew and pilots. Plenty of trained pilots.