Originally Posted by
megan
What tends to be forgotten is that the P-51 started life as a British aircraft, albeit designed and produced in the USA. It was built to specifications laid down by the British. No modification was necessary upon arrival in the UK. The P-51 came with all the items you list Harry. Windscreen was 1.5 inch armour glass,the pilots seat had a 5/16 inch plate from just below the seat to a point level with his shoulders and a 7/16 inch plate above this to protect the head, a 3/8 inch thick firewall, armour plate forward of the coolant tank, and self sealing fuel tanks. You can see the British bought their combat experience to the design.
Early versions of the P-51 had four 20mm cannon, a report written on 30 December 1942 recommended changing from the 20mm to .5 inch because,It doesn't spell it out, but infers to me that stoppages were a problem.
Stoppages always were a problem with early wing mounted Hispanos and continued to be a problem until the later Martin Baker belt feed mechanism came into use. The Westland Whirlwind which came into service around the time of the Battle of Britain had four nose mounted Hispanos and suffered with far fewer stoppages. This led to the belief that the cause of stoppages in the early Spitfires was due to the wings flexing. This may or may not have been a contributing factor as the later Hurricanes which had a stiffer wing had fewer stoppages than the Spits. However probably the most likely cause was firing while pulling more than about to two "G" which was inevitable with most deflection shooting. This problem remained with the Meteor night fighters right up until they were withdrawn in the early 1960's even though they had MB belt feed mechanisms.