Fields of Fire

Capnmac I would still differ from your explanation. Even if the 20mm shell (HE) is at the end of its range, its an explosive ordinance and relies on fragmentation to cause the greater amount of its damage. I still say that what you were talking about is the damage done by a .50 cal bullet (AP) which was the standard gun on us aircraft in WWII. Few US aircraft had 20mm cannon, The P-38, a couple of the P-39's (P-400 for one), P-61 and the Corsair F4U-1C (only 200 produced) were the only US aircraft to use it. although it was commonly used by other nations Spitfire, Bf-109, FW-190). In aircraft that had both weapons the practice was to walk the machine gun on the target and then fire the 20mm when you were on target using the machine gun tracer rounds to mark the hits. Usually there were only 20 to 40 2omm rounds against the 100 to 200 mg rounds. There was a separate switch to arm the cannon. 

I didn't mention the 37mm of the P-39 because it was like lobbing a grapefruit, hard to hit with, but one shell hit could destroy an aircraft, again because of the explosive effect and fragmentation.

Mike T.

ddp59

shell will hit point 1st not sideways as that will defeat the fuses.

It will only hit point first if it is in atmosphere allowing the aerodynamics to rule.  If it is in vacuum, aerodynamics will not come into play, thereby allowing gravity to pull the shell down to the surface with the point still pointed in the original direction it was fired.  If it was fired level with the ground the side of the shell would impact first.  If it was fired upwards, the back edge of the shell would impact first.  If there is even a little bit of air pressure present, then aerodynamics will take over and it will hit point first.

telsono

Even if the 20mm shell (HE) is at the end of its range, its an explosive ordinance and relies on fragmentation to cause the greater amount of its damage. I still say that what you were talking about is the damage done by a .50 cal bullet (AP) which was the standard gun on us aircraft in WWII.

Well, we may be dealing with apples and artichokes, too.

Air-to-air 20mm weapons differed significantly from surface-to-air weapons.  I want to remember that the aircraft weapons are Hispano-Suiza, the shipboard weapons weapons used by the USN being nearly universally Orlikons. 

Further, we clearly are not taking about the same  engagement ranges.  Air-to-air; plane on plane, the guns were set to converge at useful distances for flying, 3-500 yards out.

When on a surface vessel, you want to engage aerial  targets as far away as possible.  With the Mk 2 and later 20mm weapons that is 3000-3300 yards out, ten times aircraft dogfighting ranges.

Inverse square rule applies when dealing with the energy available to detonate a fuse train in a projectile less than 1" in diameter.  Especially a 0.27# (4.3 oz) shell with a 0.024# (1/3 ounce) HE charge.

USN pulled the 0.50 cal AAA guns very quickly from shipboard use, along with the 1.1" guns.  The .50 cal and 37mm guns had excellent use in aircraft, just not much use from ships.

Working from memory (it being long time since Surface Warfare school) the 40mm Bofors had  a surface ceiling of 6000 yards, twice that of the 20mm.  But, had even a worse record for actually detonating on contact with kamikazes, unless the round struck something substantial (landing gear, engine, main spars, etc,)

The 20x105mm round remains an excellent air-to-air weapon even today. 

The 20x72 and 20x110 shipboard weapons, not so much.

Best place to engage an aircraft aiming for your ship is when the CAP intercepts them 40-50 miles out, and the CAP adds their 1-2000 yard range to that 80-100,000 yards.  Otherwise the bakers and yeomen are  just out there creating ballistic FOD to deal with.

CapnMac - That may be the crux of the difference. Ranges of these weapons were alot shorter than the shipboard weapons. The .50cal was preferred by pilots as it was lighter, carried more ammo and therefore less of a drag on the aircraft. The US was the only air force that relied on machine guns rather than cannon as the primary armament of their aircraft at the end of WWII. The British at first used .303 cal. mg's (The Spitfire I and Hurricane I each had 8) which could saw off the wing of a bomber such as a He-111. This was fine at first, but with great fleets of bombers attacking, more bang for their buck was needed. The later series of all British aircraft had 20mm Hispano's added to their amament. The MG's being used more to target the cannon. Late in the war the Germans used their 30mm cannon (Me-262 had 4 mounted in its nose.).

Although the Russians had a good 37mm aerial cannon, the US weapon was not in the same category. When I mentioned that it was like lobbing a grapefruit, that was because of the distinct arc that it had. It was virtually impossible to hit with it. The P-39 series was the only production aircraft to use it as Bell Aircraft was a great proponent of the weapon using it on various designs from the pre-war period. 

Maximum range of aerial combat was usually limited to a maximum of 500 to 600 yards. 400 yards was the usual range for convergence of wing mounted weapons, although it is known that the better pilots like their convergence to be closer to 150 yards, but would attack even closer than that if they could. P-38 pilots liked the nose mounting of their armament which didn't need convergence with its concentrated firepower at all ranges.

Mike T.