The unbearable lightness of heavy artillery

[Bulletpoint]

On the topic of air defense, I seem to recall that AA-shells were time fuzed to burst at a specific altitude, causing a "zone of shrapnel" for any airplanes nearby? (and to prevent shells from falling back down on the city below)

[phil stanbridge]

On the topic of air defense, I seem to recall that AA-shells were time fuzed to burst at a specific altitude, causing a "zone of shrapnel" for any airplanes nearby? (and to prevent shells from falling back down on the city below)

Yeah I believe this is right. That's why you would often see 'flak clouds' appearing in particular areas of significance, ie usually in the flight path

[YankeeDog]

On the topic of air defense, I seem to recall that AA-shells were time fuzed to burst at a specific altitude, causing a "zone of shrapnel" for any airplanes nearby? (and to prevent shells from falling back down on the city below)

Heavier AAA (generally meaning stuff 75mm and up), usually yes. Heavy AAA's job is mostly to shoot at high altitude bombers, and since it takes some seconds for shells to reach the altitude of the bombers, the basic idea was to try to predict where the bomber formation was going to be some seconds into the future, and then fill that section of sky with as much steel as possible.

Major exception to this is U.S. & British heavy AAA from late 1943 on, which started to use the new Prox/VT fuse JonS mentions above -- this type of fuse actually incorporates a small radar transceiver that senses when the shell is close to an enemy plane, and detonates it appropriately. Very deadly.

Regardless, though, heavy AAA shells also usually incorporated a secondary contact fuse, in case they actually made contact with a plane before the timer fuse went off.

Light AAA was intended for use against lower altitude, maneuvering planes, so it usually relied on just a simple contact fuse and high ROF.

[Michael Emrys]

Light AAA was intended for use against lower altitude, maneuvering planes, so it usually relied on just a simple contact fuse and high ROF.

The 40 mm Bofors certainly used both a timed fuse and a contact fuse. I suspect the German 37 mm did also. I doubt smaller than that used timed fuses.

Michael

[YankeeDog]

The 40 mm Bofors certainly used both a timed fuse and a contact fuse. I suspect the German 37 mm did also. I doubt smaller than that used timed fuses.

Michael

Are you sure about that? I'm looking at a copy of TM 9-252 (1944), which is the period U.S. Military TM for the 40mm Bofors. The TM has a table of ammunition types for the 40mm Bofors, which includes among other things fuse descriptions, and for all of the listed ammunition types in the TM, the fuse is described as "superquick", with no mention of a timed option. Further, there are numerous pictures and diagrams of the 40mm cartridges in the manual and none of these diagrams or pictures show any indication of a timer ring on the nose of the projectile like you usually see with a time delay fuse. On a quick scan, I can't find any mention of setting a timed fuse in the sections on Loading and Operation, either.

Perhaps the Brits used it with time delay but the US did not? I do know that both time delay and VT fuses were developed for the 40mm *after* WWII, but I haven't heard of a time delay 40mm round that was commonly used by the U.S. military in WWII...

[YankeeDog]

Yeah... Far and away the most common fuze in use with the 40mm Bofors round was the Mk. 27:

http://uxoinfo.com/blogcfc/client/includes/uxopages/Mulvaney_Details.cfm?Ord_Id=PF23

Definitely no time delay option there; just superquick.

[JonS]

You'd be very hard pressed to set time fuzes fast enough on the quick firing LAA. They struggled to keep up with the HAA, which had a much lower ROF. In practice you'd have to either accept a ridiculously low ROF, or just not use time fuzes.

[akd]

Are you sure about that? I'm looking at a copy of TM 9-252 (1944), which is the period U.S. Military TM for the 40mm Bofors. The TM has a table of ammunition types for the 40mm Bofors, which includes among other things fuse descriptions, and for all of the listed ammunition types in the TM, the fuse is described as "superquick", with no mention of a timed option.

Probably self-destruct after a fixed time, for obvious reasons (what goes up must come down).

[YankeeDog]

Probably self-destruct after a fixed time, for obvious reasons (what goes up must come down).

No indications of anything like this on the schematics for the Mk 27 40mm fuze. I have seen this feature on fuzes for heavier AAA, tho (e.g. German 88mm, U.S. 5in.)

[YankeeDog]

You'd be very hard pressed to set time fuzes fast enough on the quick firing LAA. They struggled to keep up with the HAA, which had a much lower ROF. In practice you'd have to either accept a ridiculously low ROF, or just not use time fuzes.

Yes. 40mm Bofors has a practical ROF of about 100rnds/min/tube, and they were often used in twin and quad mountings. Hard to imagine that setting all of those fuse timers by hand would be very practical.

Similar modern systems set timed fuses via wireless electronics in the in the fire control system. But they didn't have anything like this in the 1940s...

[JasonC]

Some interesting facts about AA in WW II, from US navy stats...

It took around 500 rounds of 5 inch AA to down one enemy aircraft, as an average. That is a blend of about 300 to 1 for VT fuzes and 600 to 1 for contact or timed. 5 inch AA accounted for about 1/3rd of enemy aircraft downed by shipborn AA over the war; if 3 inch is included, heavy AA of this sort was a full third.

40mm needed on average 1750 rounds per kill 40mm accounted for slightly less than a third of AA kills.

20mm needed 7500 rounds per kill, and over 10,000 per in the earlier half of the war. But tons of it was fired and it accounted for another third, approximately, of AA kills.

50 caliber shot down very few aircraft from ground mounts, only a few percent. It needed close to 20,000 rounds bring anything down.

30 caliber was fired too, but confirmed kills by shipborn 30 cals come to less than 10 planes over the entire war. Basically stuff that light was completely useless as an antiaircraft weapon.

The vulnerability of attacking planes to shipborn AA increases significantly - by a factor of about 4 - if they were kamikazes pressing home to actual collision, rather than conventional planes dropping bombs or torpedos from some distance off. Those were also concentrated in the last year of the war when AA was heaviest.

Despite this, the hit chance of kamikazes was 8-9 times the hit rate for conventional attackers. It was only about 3% for conventional attacks, more like 1/4 for kamikazes. Conventional attacks were taken out by AA roughly 1/6 of the time, kamikazes nearly 3/4 of the time. The ratio of hits to AA losses was 1/3 for kamikazes and 1/5-6 for conventional attacks; but 4/5ths of conventional attacks had no result for either side, vs essentially zero for the kamikazes.

All things considered, medium and light AA firing huge quantities of ammo was a very effective weapon system (despite the fact they apparently never got VT fuzes - they could not be made small enough by the end of the war. The smallest shell that got them was the 3 inch AA). The guns themselves were cheap, much cheaper than the aircraft they destroyed, and they had survivability and service lives long enough to throw huge quantities of ammo and average more than a kill apiece over those service lives. As long as there were targets, that is - in the ETO the Luftwaffe was largely missing (though ground AA still shot down plenty of V-1 buzz bombs).

50 cals on the ground, on the other hand, are highly overrated as AA weapons. The effective 50 cals against aircraft were the ones in the wings of P-47s and P-51s, Hellcats and Corsairs.

FWIW...

[Michael Emrys]

Okay, see all those little black puffs? Those are from 40 mm shells. And BTW, they used automatic fuse setters that set the fuses before the four round clips were loaded into the guns.

I've seen better photos in books, but they seem to be hard to find on the web.

Michael

[JonS]

Jebus those Bettys are low! :eek:

[ArgusEye]

How can you tell? Those might easily be 5" and 3" naval dual purpose guns firing. I have seen 40mm Bofors fuse setting equipment, but never older than the 60s. Do you have any background information?

[JonS]

And BTW, they used automatic fuse setters that set the fuses before the four round clips were loaded into the guns.

I know automatic fuze setters were used. HAA used them, and they struggled to maintain their ROF, even though their ROF was much lower than LAA.

[JonS]

From here (Aug 43 T.M.):

109. AUTHORIZED ROUNDS.

a. Ammunition authorized for use in GUN, automatic, 40-mm, M1, is listed in table I and illustrated in figures 205 to 207. It will be noted that the nomenclature (standard nomenclature) completely identifies the round. The numbers in parentheses preceding the nomenclature refer to assembly numbers in table II, which contains ammunition data.

TABLE I - AUTHORIZED ROUNDS

SERVICE AMMUNITION

(1) CARTRIDGE, AP-T, M81A1, 40-mm AA. guns

- CARTRIDGE, AP-T, M81A1, steel case, 40-mm AA. guns

(2) CARTRIDGE, AP-T, M81, 40-mm AA. guns

(3) CARTRIDGE, HE, Mk. I (Navy), w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns

(4) CARTRIDGE, HE-T (SD, M3), Mk. II, w, FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)

- CARTRIDGE, HE-T (SD, M3), Mk. II, steel case, w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)

(5) CARTRIDGE, HE-T (SD), Mk. II, w/FUZE, P.D., M71, 40-mm AA. guns (muzzle velocity 2,700 f, s)

(6) CARTRIDGE, HE-T (SD, M3), Mk. II, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,700 f/s)

- CARTRIDGE, HE-T (SD, M3), Mk. II, steel case, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,700 f, s)

(7) CARTRIDGE, HE-T (SD, No. 12), Mk. II, w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)

- CARTRIDGE, HE-T (SD, No. 12), Mk. II, steel case, w/FUZE, PD., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)

(8) CARTRIDGE, HE-T (SD, M3), Mk. II, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)

- CARTRIDGE, HE-T (SD, M3), Mk. II, steel case, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)

(9) CARTRIDGE, HE-T (SD, No. 12), Mk. II, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)

- CARTRIDGE, HE-T (SD, No. 12), Mk. II, steel case, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)

(10) CARTRIDGE, HE-T (SD, No. 12), Mk. II, w FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,870 f/ s)

- CARTRIDGE, HE-T (SD, No. 12), Mk. II, steel case, w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,870 f, s)

(11) CARTRIDGE, HE-T (SD), Mk. II, w/FUZE, P.D., 251, Mk. I, 40-mm AA. guns (muzzle velocity 2,870 f, s)

- CARTRIDGE, HE-T (SD), Mk. II, steel case, w/FUZE, P.D., 251, Mk. I, 40-mm AA. guns (muzzle velocity 2,870 f/s)

PRACTICE AMMUNITION

(12) CARTRIDGE, TP-T, M91, w FUZE, dummy or inert, M *, 40-mm AA. guns (muzzle velocity 2,700 f, s)

(13) CARTRIDGE, HE-T, Mk. II, inert loaded, w/FUZE, dummy or inert, M *, 40-mm AA. guns (muzzle velocity 2,700 f, s)

DRILL AMMUNITION

(14) CARTRIDGE, drill, M17, 40-mm AA. guns

--------------------------------------------------------------------------------

*-FUZE, dummy, M69; or inert FUZE, P.D., M64, M64A1, Mk. 27, 251 Mk. I, or other suitable types may be assembled to the projectile.

Note that all the fuzes are all PD, and that the service rounds are all tracer. There is a distinct lack of tracer trails in those photos.

[YankeeDog]

How can you tell? Those might easily be 5" and 3" naval dual purpose guns firing. I have seen 40mm Bofors fuse setting equipment, but never older than the 60s. Do you have any background information?

+1... What leads you to conclude those are 40mm airbursts, Michael?

Of course, l've seen hundreds of shots showing those "little black puffs" around U.S. ships in the Pacific. They're amongst the more iconic images from the PTO. But I don't remember a single caption that specifically identifies them as 40mm airbursts. They could be from 5" and 3" guns. Bear in mind that U.S. Battleships had as many as 20 5-inch guns, Fleet carriers and cruisers usually had 8-12, Destroyers had 5-6, and even transports and other non-combat hulls usually had 1 or 2. So even a relatively small U.S. Navy flotilla had a *lot* of 3" and 5" guns. And those 5"/L38s had a burst ROF of 15rds/min. It's therefore completely plausible that all of those "little black puffs" could be from the 5" and and 3" in a shells, rather than 40mm.

Until a few years ago, if you had asked me I would have guessed the 40mm had a timed fuse option as well. But I learned that my grandfather had commanded a 40mm battery aboard the USS Baltimore and I was curious to learn more about what he did during the war so I dug up the TM for the 40mm, amongst other references. And I can find no mention of a WWII-era timed fuse round for the 40mm anywhere, nor can I find mention of setting timed fuses in the procedures sections of the manuals. As I already mentioned, schematics for the most common fuse for the 40mm, the Mk. 27 (over 9 million produced during the war) do not show a timed fuze capability, only superquick impact.

If you have info to the contrary, I'd love to see it. But considering all other evidence I've found to date points the other way, I'm afraid I can't just take your word for it.

[Michael Emrys]

How can you tell? Those might easily be 5" and 3" naval dual purpose guns firing.

That's an awful lot of 5" and 3" guns firing awfully fast, don't you think? Look at the pictures again. Like I say, there are better pics that show both 5" and 40 mm bursts, and they are very distinguishable.

Michael

[YankeeDog]

That's an awful lot of 5" and 3" guns firing awfully fast, don't you think?

Yep. See above.

Look at the pictures again. Like I say, there are better pics that show both 5" and 40 mm bursts, and they are very distinguishable.

I have a full-page plate of that picture of Bettys attacking the Guadalcanal landing fleet on 8/8/1942 in one of my books. Damned if I can see a difference which indicates that some are 40mm and some are 5in. Some are definitely bigger than others, but that could be because they're older (more dispersed), or closer to the camera, or some other factor; I can't tell.

And actually, now that I think of it, those flak puffs in the 8/8/1942 image almost certainly are not 40mm, for the simple reason that the 40mm Bofors had not yet reached wide deployment in mid-1942 -- AFAIK, most of the U.S. warships at the Guadalcanal landings still had the older 1.1" guns as their mid-size AAA complement.

[JasonC]

Guys - the 40mm tracer was designed to burn for a fixed time, and then burn through to the HE charge, making the shell self-destruct at its intended maximum range. This was primarily to ensure that the round would not fall "live" on other ships in the fleet or other friendlies on the ground. A secondary result would be to scatter fragmentation in the air in a curtain at that max range. In USN use, that max range was about 5000 yards.

If you want a web reference, check this page -

http://www.navweaps.com/Weapons/WNUS_4cm-56_mk12.htm

[JonS]

A self destruct mech at a fixed range is not really the same thing as a set-able time fuze.

[womble]

A self destruct mech at a fixed range is not really the same thing as a set-able time fuze.

Would lots of misses (a fact of life for AAA) produce the "puffball field" we see in the photo? How much variation in the burn-through would it take to smear the self-destruct over enough time and space to produce that piccy? With several ships firing from different angles at the approaching t-bombers, and the ships moving, could Emrys be right without 40mm needing to have a settable timer fuse?

[YankeeDog]

First of all, those TBs in the first photo are flying extremely low; the guns would have been firing near or in some cases probably even below zero elevation. So the vast majority of any 40mm ordnance fired at them would have fallen into the sea long before self-destruct.

Second, the tracer burnout/self-destruct mechanism was not a precision fuze and had a pretty broad variability -- 8-12 seconds from what I've read. So any airbursts from terminal self destruct would be quite spread out -- depends a bit on trajectory, but as a SWAG a 40mm round is probably going to travel over 2000m in that 4 second time window. The flak clouds in those photos actually pretty organized and tight as flak clouds go; they have all of the hallmarks of organized, deliberately planned flak.

Finally, once again, there WEREN'T very many, if any, 40mm Bofors guns off of Guadalcanal in mid-1942. 40mm Bofors were just starting to enter service in 1942, and most of the initial production went onto ships then under construction -- most ships built pre-war weren't retrofitted with them until late 1942 or 1943. So whether you think the 40mm had a time delay fuse or not, the Flak in the first photo taken on 8/8/1942 *can't* be 40mm airbursts, because there were few, if any 40mm Bofors in the Solomons at that time.

The other two photos are from the Battle of Santa Cruz (25-27 Oct. '42), and by this time somewhat more U.S. ships did have 40mms -- the Enterprise is the carrier shown in those photos, and she was partially refitted with 40mms in Sept. 1942, though at this point she had comparatively few of them -- the Sept. '42 refit gave her 16 40mm tubes (4xquad), but by the end of the war, the Lucky E was sporting 54 40mm tubes in a combination of twin and quad mounts (!).

But many of the other U.S. ships at the Battle of Santa Cruz were still carrying the older 1.1" mounts -- at a quick scan, I can verify the USS Hornet, USS Portland, USS San Juan, USS Porter, and USS Shaw all still had 1.1" guns at this time. Probably others as well; I'd have to dig more to establish a complete picture of the AAA armament of the US TFs at this battle. In any event, even in the Santa Cruz photos, I think it's unlikely a majority of those flak puffs could possibly be from 40mm, simply based on the number of 40mm tubes present on the U.S. ships at that battle (assuming, arguendo, that a time delay fuse existed for the 40mm, which AFAICT, it did not).

[Michael Emrys]

First of all, those TBs in the first photo are flying extremely low; the guns would have been firing near or in some cases probably even below zero elevation. So the vast majority of any 40mm ordnance fired at them would have fallen into the sea long before self-destruct.

Forget that photo. I should not have used it and would not if more pics could have been found in the limited time I had to search.

Second, the tracer burnout/self-destruct mechanism was not a precision fuze and had a pretty broad variability -- 8-12 seconds from what I've read. So any airbursts from terminal self destruct would be quite spread out -- depends a bit on trajectory, but as a SWAG a 40mm round is probably going to travel over 2000m in that 4 second time window.

The American Arsenal lists maximum range as horizontal: 10,850 yds vertical: 7,625. That should work out to about a five second burn or a bit less.

Finally, once again, there WEREN'T very many, if any, 40mm Bofors guns off of Guadalcanal in mid-1942.

Don't obsess over Guadalcanal. That is a dead horse. My apologies for dragging it into the discussion in the first place.

The other two photos are from the Battle of Santa Cruz (25-27 Oct. '42), and by this time somewhat more U.S. ships did have 40mms -- the Enterprise is the carrier shown in those photos, and she was partially refitted with 40mms in Sept. 1942, though at this point she had comparatively few of them -- the Sept. '42 refit gave her 16 40mm tubes (4xquad), but by the end of the war, the Lucky E was sporting 54 40mm tubes in a combination of twin and quad mounts (!).

But many of the other U.S. ships at the Battle of Santa Cruz were still carrying the older 1.1" mounts -- at a quick scan, I can verify the USS Hornet, USS Portland, USS San Juan, USS Porter, and USS Shaw all still had 1.1" guns at this time. Probably others as well; I'd have to dig more to establish a complete picture of the AAA armament of the US TFs at this battle. In any event, even in the Santa Cruz photos, I think it's unlikely a majority of those flak puffs could possibly be from 40mm, simply based on the number of 40mm tubes present on the U.S. ships at that battle (assuming, arguendo, that a time delay fuse existed for the 40mm, which AFAICT, it did not).

The South Dakota was there and providing close support to the Enterprise. It apparently sported a total of 68 40 mm guns. More than enough to produce the clouds we see in the pics.

Michael

[YankeeDog]

The South Dakota was there and providing close support to the Enterprise. It apparently sported a total of 68 40 mm guns. More than enough to produce the clouds we see in the pics.

Not that many at the time. Much like the Enterprise, the South Dakota was originally launched with 1.1" guns (one of the last ships built by the U.S. to be fit with 1.1" as part of her original complement, actually), and was partially refit with 40mms in the fall of '42, just in time for the Battle of Santa Cruz. According to her history, a the time she was carrying total of 10x40mm quad (40 tubes total). The 68x40mm was a later war refit.

But regardless, between the four quad mounts on the Lucky E and the ten the South Dakota, I will happily admit that this is a fair number of 40mm tubes. If they had time delay fuzes, these guns might well have been able to produce a fair number of airbursts...

So let us turn the discussion away from the balmy shores of Guadalcanal and the azure blue waters of Ironbottom Sound. You still haven't rebutted the total absence of a time delay fuze for the 40mm on ordnance lists, and a complete lack of any mention of calculating or setting time delay in the training and technical manuals for the 40mm. A safety self destruct feature on tracer burn-out definitely does not count; this is not something that could have been used to create a targeted flak field.