37x145mmR HE shell vs 30×90RB mine-shell

[jmcalli2]

The 25-30 kg gun and it's ammo can be installed on most of fighters from second half of the 1930s without much of problems (even on the small Bf 109, I-16 or MB.152), not the case with a 100 kg gun and it's ammo.

The M4 - M10 37mm gun was used on the P-38 (early versions), P-39, and P-63.
The P-38 was similar in size to the Me-110.
The P-39 was similar in size to the Me-109.
The P-63 was similar in size to the Fw-190.

The Germans problems were a reliance on types designed to carry 7.92mm guns. They had to adapt them for the heavier weapons needed to complete the bomber interception mission.
The same problem was run into by the P-36 and P-40; designed for .30cal and adapted to .50cal weapons.
The P-38, P-39, and P-63 were designed to intercept bombers and carried heavy cannon from the start.

 

[tomo pauk]

The M4 - M10 37mm gun was used on the P-38 (early versions), P-39, and P-63.
The P-38 was similar in size to the Me-110.
The P-39 was similar in size to the Me-109.
The P-63 was similar in size to the Fw-190.

The Germans problems were a reliance on types designed to carry 7.92mm guns. They had to adapt them for the heavier weapons needed to complete the bomber interception mission.
The same problem was run into by the P-36 and P-40; designed for .30cal and adapted to .50cal weapons.
The P-38, P-39, and P-63 were designed to intercept bombers and carried heavy cannon from the start.

M10 gun was never installed in P-38 or P-39. German aircraft predated the US aircraft with regard to introduction of cannon armament as a regular, everyday armament.
One can install pretty much any ww2 autocannon on a 2-engined ww2 fighter, problem was how to install a it on a 1-engined fighter. P-39 and P-63 were pretty much designed around the cannon, and were able to carry exactly 1 of those. Compare the P-63 with Fw 190 that can carry 4 cannons, two of them MK 108 cannons of 30mm calibre, in a wing that was 20% smaller than on the P-63. The Bf 109 was able to carry 3 cannons, wing being 80% of area of what P-63 had. See the Spitfire - 4 20 mm cannons + 4 LMGs in the wing; tiny MB.152 carried 2 big HS 404s in the wing (that were still smaller than M4s).
37mm M4 was never a retrofit for existing fighters (for practical reasons of both size and weight, both of cannon and it's ammo), unlike the 20 or 30 mm cannons. It was 20mm that was replacing the 37mm on US aircraft.

With all of this said, it was too bad that, for installation on aircraft, Americans didn't bought both the cannons and licence for production at Oerlikon in the second half of 1930s. Would've saved them a lot of problems both with Hispano and M4.

 

[jmcalli2]

M10 gun was never installed in P-38 or P-39.

The M4 was. The M10 was installed on the P-63 and was nearly identical to the M4; the difference was the M10 had the ability to uses linked ammunition, nearly doubling the number of rounds carried. Are you thinking of the M9? Totally different and much heavier weapon based on the 37mm AA gun.