What about the 2pdr uncapped AP shot hitting the German face hardened armor?
Bad news for the 2-pdr, although arguably an ammunition and not a gun issue itself. The FH armour was pretty much impenetrable to the uncapped AP shot, as Blutarski's and the Russian data shows. FH armour became pretty universal from January 1942 in the desert as most if not all the older vehicles had been lost by December.
There's an overview of the issue here: link
There is a good thread on Missing Lynx that discusses Panzer III variants in the desert in 1941 in exhaustive detail.
link
My current understanding is that by CRUSADER most of PR5 and a small part of PR8 consisted of Panzer IIIG which were vulnerable to the 2-pdr and the US 37mm M3 over all sides and at normal combat ranges. Most of PR8 and a small part of PR5 consisted of Panzer IIIH which were not vulnerable over the frontal arc. The Panzer IV was vulnerable over the frontal arc unless it had bolt-on armour which would reduce the area of vulnerability to the turret front (a small target), but there were so few, and they were used in a way that makes this irrelevant. Almost all of these vehicles were lost during CRUSADER and the Panzer III replacements were Panzer IIIJ (short) which were no longer vulnerable over the frontal arc. This royally screwed 1st Armoured Division in January 1942.
In terms of awareness, most of the German tanks encountered in combat in 1941 prior to CRUSADER were PR5 tanks as PR8 only got into the act in BATTLEAXE, and it appears the right lessons were not learned from this. It was thus reasonable to presume for the British authorities at the start of CRUSADER that the 2-pdr (and the similar M3 37mm) was a good enough gun and that the delays in shipping 6-pdrs were not a major concern.
That's the potted and somewhat complicated history as far as I can make it out. I have documented this here, and even though 4 Armoured Bde did not have 2-pdr armed tanks, the principle applies: link
All the best
Andreas
