Rn vs IJN

[Thumpalumpacus]

Yes I understand the nature of SAMs, cruise missiles, Ballistic missiles etc. The heavy machine gun was however, generally effective as light AA against WW2 aircraft. Kamikaze were a special case. The M16 GMC (quad .50 on a half-track) were extremely effective against low flying aircraft in Europe. Caused some unfortunate friendly fire losses too. But they shot down quite a few Fw 190s for example. Quite effective against ground targets as well.

I always had an irrational love for the Meat-Chopper.

 

[ThomasP]

The use of gasoline may have just been a holdover from the US Army mountings, since they were considered experimental on the ships, so maybe not worth the time and effort to run power leads. Or it may have been that the USN was looking at local power control like the RN had been using. At some point the RN switched over to local power control for most of the quadruple and octuple 2pdr mounts on cruisers and larger, and on new build DDs. They retrofitted the power system to many of the older mounts as time permitted.

I believe all of the RN Mk IV 'Hazemeyer' and Mk V twin 40mm Bofors mounts were installed with local power.

Even the little Mk V 'scooter' 20mm twin mounts and the Mk V 'Boffin' single 40mm Bofors mounts had the local power option also, though I do not know how common the generator package was vs remote power.

20mm twin Mk V 'scooter' mount

40mm single Mk V 'Boffin' mount

Incidentally, the 'tombstone' magazines used on the Maxon were a transfer of equipment from the USN pre-war and early-war equipment used with the .50 cal water-cooled single and twin mounts.

.50 cal twin Mk 22 mount (water-cooled)

 

[z42]

The heavy machine gun was however, generally effective as light AA against WW2 aircraft. Kamikaze were a special case.

IIRC the USN didn't think so, and started replacing the 50 cals with the 20mm Oerlikons long before kamikazes came into being.

The M16 GMC (quad .50 on a half-track) were extremely effective against low flying aircraft in Europe. Caused some unfortunate friendly fire losses too. But they shot down quite a few Fw 190s for example. Quite effective against ground targets as well.

Was it "extremely effective" because the HMG caliber is in some sense the "sweet spot", or because the US produced an ungodly amount of them and sprinkled them everywhere?

In the early 1950'ies, presumably based on WWII experience as well as faster jets being introduced, Oerlikon calculated the sweet spot for a gun based AA was 35 mm, leading to the famous Oerlikon 35 mm which is still in use.

 

[Greg Boeser]

Yes I understand the nature of SAMs, cruise missiles, Ballistic missiles etc. The heavy machine gun was however, generally effective as light AA against WW2 aircraft. Kamikaze were a special case. The M16 GMC (quad .50 on a half-track) were extremely effective against low flying aircraft in Europe. Caused some unfortunate friendly fire losses too. But they shot down quite a few Fw 190s for example. Quite effective against ground targets as well.

I've seen .50 caliber AA described as revenge weapons. Because by the time the target was in effective range, you were already dead.

 

[Wild_Bill_Kelso]

IIRC the USN didn't think so, and started replacing the 50 cals with the 20mm Oerlikons long before kamikazes came into being.



Was it "extremely effective" because the HMG caliber is in some sense the "sweet spot", or because the US produced an ungodly amount of them and sprinkled them everywhere?

I generally base such statements on operational histories, as in enemy units destroyed. Of which that particular vehicle did clearly produce notable results, such as during Operation Bodenplate. It seems that a couple of these things could fairly well deny a given area to low flying enemy aircraft, at that time.

In the early 1950'ies, presumably based on WWII experience as well as faster jets being introduced, Oerlikon calculated the sweet spot for a gun based AA was 35 mm, leading to the famous Oerlikon 35 mm which is still in use.

I appreciate the data, but I did specify, WW2... I grasp very well the notion that jets required different kinds of countermeasures.

 

[Wild_Bill_Kelso]

I've seen .50 caliber AA described as revenge weapons. Because by the time the target was in effective range, you were already dead.

That does not appear to have been the case in reality.

 

[Glider]

That does not appear to have been the case in reality.

It might have been Revenge in the sense that you are still alive to shoot the plane down, but as the aircraft would have already have dropped its bomb, or torpedo, you were about to die.

 

[Shortround6]

I would note that the US Army did not field a 20mm ground gun.
So the choice was a multiple .30 cal (not used), the multiple .50 cal or a single 37mm or combination mount.

The US Army, aside from aircraft, did not have the 20mm ammo in the supply system.

The quad mount was a quick change from the twin mount when they figured the powered mount was too much mount for too little gun. The gun mount was also put on a trailer which is where the gasoline engine comes from.

Ship and land use were a little different. Crashing airplane on a ship could still hit the ship 300-500ft away and could result in the gunners (and rest of crew) swimming in a short period of time (even a few hours). Crashing plane on land does not have that result. It may kill or wound/injury a small number of people.

IN 1945 in the Pacific even the navy thought the 20mm AA guns were revenge weapons.

 

[Wild_Bill_Kelso]

It might have been Revenge in the sense that you are still alive to shoot the plane down, but as the aircraft would have already have dropped its bomb, or torpedo, you were about to die.

Yeah I got the idea, and that may be more relevant on a ship at least in some cases, but it did not appear to be the case on land at any rate. For one thing the AA was not always at the location of the target.

I assumed we were all on the same page on this already, but apparently not so forgive me for spelling it out.

This was also how it works with ships too, as defensive warships like cruisers and destroyers were often positioned around, and at some distance from (as in miles) the primary target - which might be an aircraft carrier, a troop transport or supply ship etc. Standard US navy formations for a carrier task force in WW2 were around 12,000 yards wide. With really large task forces they got a lot bigger than that. Many WW2 aircraft that attacked ships did so with torpedo attacks, rocket attacks, or strafing, which had to be done from quite close and at low altitude. Torpedo runs in particular required not only low but slow, particularly during the early years of the war (this improved later with the wooden carapice they added to them, allowing higher speed and higher altitude drops). So these aircraft most certainly were vulnerable to heavy machine guns and in fact, were routinely destroyed by them.

When it comes to smaller caliber ordinance like the .50 caliber or any other machine gun or light cannon, right up to the 20mm Oerlikons, quite often the individual doing the shooting is not even aboard the target. Or, some are but not the majority of them. Similarly, on land, those MGMC 16 and MGMC 15 (same thing but two HMG and a 37mm gun) gun carriages were positioned around what were considered to be the intended targets - which might be an airfield, a supply dump, a railhead, a marshaling point, a column of tanks, a bridge, etc. Those things were pretty small too and may not even be visible to the attacking aircraft until they are already within it's line of fire.

Dive bombers are harder to hit than torpedo bombers, especially during their dive. A kamikaze attacking a ship is a bit trickier still. In both cases I can definitely understand why you would want to put the emphasis on larger caliber guns. By the time you get to jets, as I assume everyone here knows, the emphasis shifted again to very high speed radar controlled (and later autonomous) missiles, with much less emphasis on guns of any kind, since the speed of the incoming threat (whether an aircraft or cruise missile or ballistic missile) is too high to hit with most guns, barring CIWS etc.

 

[Shortround6]

To get somewhat back on track the Japanese went with the Hotchkiss 13.2mm machine gun.
Hotchkiss salesman was either very, very good or offered a really good kickback deal (both?).
Gun in French service

Japanese moved the gunner to the side.

Gun came in single, twin, triple and quad mounts. Magazines held 30 rounds. About as powerful as the US .50 per round but nowhere near the amount of fire power per minute.
For those officers who believed that belt feed was just a fad and not really here to stay.

 

[Glider]

If I remember correctly Israel modified these quad 0.5 to twin 20mm with some success.

 

[Shortround6]

This was also how it works with ships too, as defensive warships like cruisers and destroyers were often positioned around, and at some distance from (as in miles) the primary target - which might be an aircraft carrier, a troop transport or supply ship etc. Standard US navy formations for a carrier task force in WW2 were around 12,000 yards wide. Many WW2 aircraft that attacked ships did so with torpedo attacks, rocket attacks, or strafing, which had to be done from quite close and at low altitude.

The .50 cal and 20mm guns were pretty much for the defense of the individual ship. The bigger guns were much more often used for "fleet" defense or at least formation defense.

The "effective" range of these guns was pretty much around 1000yds. This was due to primitive sights, and the reliance on tracer ammunition. Tracers at 1000 yds tell you where you should have been aiming 2 seconds ago. We can go back and forth about max range and and bunch other useless data but the 1000yd figure came from a several navies after some hard won experience. Ships have weight limits and crew limits. The small guns took up too much space/weight for the target effect. The complicated manual gun mounts took up too much space/weight for the target effect. A faster slewing powered mount (with a better sight) and a smaller crew was much more effective on a space/weight evaluation.

The coordination between ships was pretty dismal. Ships were often spaced several thousand yds apart to reduce collisions.

The Army didn't have to worry about the ground flipping over in bad weather if they parked too many vehicles per acre.

 

[z42]

I generally base such statements on operational histories, as in enemy units destroyed. Of which that particular vehicle did clearly produce notable results, such as during Operation Bodenplate. It seems that a couple of these things could fairly well deny a given area to low flying enemy aircraft, at that time.

Note that I wasn't claiming they didn't work. My claim is that 12.7mm was on the small side for a really good aa weapon in WWII. Still, having something is a lot better than being without. And if you have lots of it, sure you're bound to see some results.

(The Germans considered their 20mm flak to be a somewhat marginal weapon already early in the war, due to lack of range and punch. The quad 20 mount extended the life of the 20mm as an AA weapon, although the 37mm was considered the better solution.)

 

[Glider]

The one aircraft that the quad 0.5 would have had considerable difficulty with would have been a heavily armoured aircraft such as the Hs 129. Fortunately this was never a real issue

 

[z42]

I would note that the US Army did not field a 20mm ground gun.
So the choice was a multiple .30 cal (not used), the multiple .50 cal or a single 37mm or combination mount.

They did field the 40mm Bofors, which apparently largely replaced the 37mm by mid-war. Which, just like the naval version, was an excellent AA weapon.

 

[Wild_Bill_Kelso]

The one aircraft that the quad 0.5 would have had considerable difficulty with would have been a heavily armoured aircraft such as the Hs 129. Fortunately this was never a real issue

I seriously doubt it. Armor doesn't make an aircraft immune to bullets, especially heavy machine gun bullets.

 

[Wild_Bill_Kelso]

Note that I wasn't claiming they didn't work. My claim is that 12.7mm was on the small side for a really good aa weapon in WWII. Still, having something is a lot better than being without. And if you have lots of it, sure you're bound to see some results.

(The Germans considered their 20mm flak to be a somewhat marginal weapon already early in the war, due to lack of range and punch. The quad 20 mount extended the life of the 20mm as an AA weapon, although the 37mm was considered the better solution.)

I think AA defense was typically layered. Heavy machine guns (and 20mm cannon) have the role of hitting lower and closer targets. 3", 5", 88mm, 90mm etc. are for much more distant (and usually high flying) targets. 57mm, 40mm and 37mm (etc.) are in between.

Air defenses in WW2 typically included all three categories, if there were sufficient resources.

Early close-in AA was often just .30 caliber machine guns. Which might be in a single mount.

With vehicles there is also of course a tradeoff between the size of the weapon carried and the amount of ammunition it uses, with range and power (one shot destruction).

Obviously the mutli-barrel weapons greatly increased the viability of these lighter weapons. Both the quad 50 and the quad 20mm were considered quite dangerous by pilots, I can promise you that.

 

[Shortround6]

I think AA defense was typically layered. Heavy machine guns (and 20mm cannon) have the role of hitting lower and closer targets. 3", 5", 88mm, 90mm etc. are for much more distant (and usually high flying) targets. 57mm, 40mm and 37mm (etc.) are in between.

You are correct however the 57mm was pretty much non-existent in WW II, They fooled around with them but very, very few were deployed.
As very general rule of thumb the weight of the shell and weight of the gun (and the weight of mounting ) went up with cube of caliber. A 40mm was eight times as heavy as a 20mm.
This assumes the gun and mount allowed for and equal rate of fire

I was looking at the entry for the US 1.1in gun on Nav weapons and unfortunately the ballistics table is all screwed up.
I have moved some of the columns to where they should be. It explains a lot about actual effective range.
Just look at the figures for 2,000yds. Now figure that a 300mph plane is moving at 440fps (over a 1/4 mile) before the shell reaches it and you are using one of those cartwheel sights, from a moving deck and you have no range finder, you don't actually know how far away the plane is.

Range with HE with MV = 2,600 fps (792 mps) 1c 2c

Elevation	Distance	Striking Velocity	Angle of Fall	Time of Flight	Maximum Ordinate
0.52 degrees	1,000 yards (914 m)	1,818 fps (554 mps)	0.67 degrees	1.37 seconds	8 feet (2.4 m)
0.90 degrees	1,500 yards (1,372 m)	1,470 fps (488 mps)	1.35 degrees	2.32 seconds	22 feet (7 m)
1.45 degrees	2,000 yards (1,839 m)	1,177 fps (359 mps)	2.42 degrees	3.47 seconds	51 feet (16 m)
5.52 degrees	4,000 yards (3,658 m)	775 fps (236 mps)	11.37 degrees	9.97 seconds	442 feet (135 m)
14.60 degrees	6,000 yards (5,486 m)	491 fps (150 mps)	34.85 degrees	21.10 seconds	1,920 feet (585 m)
40.88 degrees	7,400 yards (6,767 m)	434 fps (132 mps)	78.45 degrees	47.70 seconds	8,600 feet (2,621 m)
90.00 degrees	N/A	N/A	N/A	N/A	19,000 feet (5,791 m)

Nav/weps has a similar table for the 20mm Oerlikon

USA 20 mm/70 (0.79") Oerlikon Marks 1, 2, 3 and 4 - NavWeaps

navweaps.com

Just hint. time of flight to 2,000yds is 5.01 seconds.

Even a Swordfish is going to move over 900ft in that amount of time.

 

[Wild_Bill_Kelso]

You are correct however the 57mm was pretty much non-existent in WW II, They fooled around with them but very, very few were deployed.
As very general rule of thumb the weight of the shell and weight of the gun (and the weight of mounting ) went up with cube of caliber. A 40mm was eight times as heavy as a 20mm.
This assumes the gun and mount allowed for and equal rate of fire

I was looking at the entry for the US 1.1in gun on Nav weapons and unfortunately the ballistics table is all screwed up.
I have moved some of the columns to where they should be. It explains a lot about actual effective range.
Just look at the figures for 2,000yds. Now figure that a 300mph plane is moving at 440fps (over a 1/4 mile) before the shell reaches it and you are using one of those cartwheel sights, from a moving deck and you have no range finder, you don't actually know how far away the plane is.

Range with HE with MV = 2,600 fps (792 mps) 1c 2c

Elevation	Distance	Striking Velocity	Angle of Fall	Time of Flight	Maximum Ordinate
0.52 degrees	1,000 yards (914 m)	1,818 fps (554 mps)	0.67 degrees	1.37 seconds	8 feet (2.4 m)
0.90 degrees	1,500 yards (1,372 m)	1,470 fps (488 mps)	1.35 degrees	2.32 seconds	22 feet (7 m)
1.45 degrees	2,000 yards (1,839 m)	1,177 fps (359 mps)	2.42 degrees	3.47 seconds	51 feet (16 m)
5.52 degrees	4,000 yards (3,658 m)	775 fps (236 mps)	11.37 degrees	9.97 seconds	442 feet (135 m)
14.60 degrees	6,000 yards (5,486 m)	491 fps (150 mps)	34.85 degrees	21.10 seconds	1,920 feet (585 m)
40.88 degrees	7,400 yards (6,767 m)	434 fps (132 mps)	78.45 degrees	47.70 seconds	8,600 feet (2,621 m)
90.00 degrees	N/A	N/A	N/A	N/A	19,000 feet (5,791 m)

Nav/weps has a similar table for the 20mm Oerlikon

USA 20 mm/70 (0.79") Oerlikon Marks 1, 2, 3 and 4 - NavWeaps

navweaps.com

Just hint. time of flight to 2,000yds is 5.01 seconds.

Even a Swordfish is going to move over 900ft in that amount of time.

Well, if you ever went duck hunting, you know you have to lead a target.

I think you are very much overstating the role of picket warships upthread a bit, but ... it's ok.

 

[Shortround6]

Well, if you ever went duck hunting, you know you have to lead a target.

Well, there is leading it and there is leading it by 25 times it's own body length
(Swordfish at 2,000yds doing 130mph)

I think you are very much overstating the role of picket warships upthread a bit, but ... it's ok.

Picket ships were supposed to be early warning. They were not the outer ring of the AA defenses.
And a lot depends on the navy and the timing (which year).

RN destroyers could not use their own 4.7 in guns to shoot at aircraft flying over them. Max elevation was 40 degrees for all the pre-war stuff. They could shoot at planes that were around 10,000ft high over ship several miles away. At least that was the theory. Now try it when the planes are coming from the opposite side of the target ship. Yes they could shoot at lower flying planes (torpedo bombers, low level bombers). Against dive bombers or any plane doing an above 40 degree attack most of the old (pre Tribal class) British destroyers only had either two 2pdr guns (the old ones) or two quad .5in mounts until 1939/40. Ability to present massed high angle (over 40 degrees) from destroyers was pretty much non-existent.
No data sharing
Tribals got a quad 2pdr and were pretty hot stuff. And they got the two quad .5in MGs, which were replaced/supplemented by 2-4 20mm guns.
In spite of using a better AA director for the main guns (for helping out their buddies) all of the Tribals had one twin 4.7 mount taken off and replaced by by a twin 4in mount for high angle fire.

US didn't get into war, as we all know, until the end of 1941. US air defense practice took a while to evolve and the US was actually ahead of everybody else. What the US was doing in 1944/45 was way different that what everybody else was doing in 1939-42.