Dive bomber accuracy in perspective.

[EwenS]

I do like this bit from the original British author.

But that author was someone looking at the USN position from the outside. And it is easy to see why he might have arrived at that conclusion when you look at USN fighter procurement during the 1930s.

Grumman F2F-1 entered service early 1935. Still in front line service with VF-2 in 1940.
Grumman F3F-1 entered service in the first half of 1936. Still in front line service in 1940, with versions with uprated engines arriving in 1937 (F3F-2) and Dec 1938 (F3F-3) but not in sufficient numbers to replace everything that had gone before.

Then the Brewster F2A Buffalo entering service from June 1940 with a single squadron and still on the front line with the USN in early 1942 in its later versions. With the F4F entering service from Dec 1940.

When you consider that in 1940/41 only just over 400 F4F were built between 1 July 1940 and 31 Dec 1941, and ranging betwen 1 & 47 aircraft per month, and then figure in the exports, it is easy to see why more Martlets were not forthcoming from the USA in 1941, even before all the various modifications were made. Monthly production only reached 3 figures in May 1942.

 

[EwenS]

Friedman in " Naval Anti-Aircraft Guns and Gunnery" makes this comment about the USN experience in the first 8 months of 1942 based on a report issued by COMINCH in Nov 1942 (with my emphasis).

"Contact with the Royal Navy revealed that the speed of modern air-surface warfare was far beyond that for which US equipment had been designed. Anti-aircraft doctrine had to be changed radically so that batteries could become effective against fast-moving and fast-breaking attacks. Ship's organisations had to be changed to permit higher conditions of anti-aircraft readiness. Communications within ships had to be made more effective. Radical steps(presumably radar) were needed to obtain accurate ranges. The USN was badly deficient in light anti-aircraft weapons. In medium-calibre weapons it had bought the right kind of guns, but in insufficient quantity...."

The USN studied the effectiveness of its AA fire. It was mid-1944 however before the 5"/38 exceeded the performance of the 20mm in terms of aircraft shot down. Something no doubt helped by the increasing availibility of the VT fuse.

 

[Reluctant Poster]

Full disclosure: I have a soft spot in my head for the SBD.

I believe the F4F did indeed stop an attack cold against U.S.S. Lexington (possibly the second wave too).

There was only one Japanese wave at Coral Sea and that was very successful. Two torpedoes into Lexington, two bombs into Lexington and one bomb into Yorktown. Lexington sustained several near misses. Yorktown also sustained several near misses, two of which were particularly damaging.
From Lundstrom "First Team": "Thus the combat air and anti-torpedo-plane patrols destroyed three of the eighteen Japanese carrier attack planes. Antiaircraft fire would have to do the rest."
For the dive bomber attack on Lexington, he writes: "The Japanese escort had soaked up the attention of the interceptors and cleared the way for the dive bombers to approach the task force without interference." "Undisturbed by enemy fighters the nineteen Shokaku carrier bombers deployed into a long string in final preparation for their dives."
For the dive bomber attack on Yorktown, he writes: "At 1124, the first Zuikaku kanbaku peeled off to dive. Meanwhile McCormack and Haas just had passed 13,000 feet when they spotted below and slightly ahead the long string of enemy dive bombers waiting their turn to attack." "Although the Zuikaku carrier bombers did not lose any of their numbers to fighter attack, McCormack's ambush certainly did not help their accuracy against the Yorktown." " They claimed between eight and ten hits on a Yorktown-type carrier", but actually got only one, because of the crosswind dives, Buckmaster's skillful ship handling and section "Wildcat Brown.""
At Midway the Hiyru managed to launch two waves. The first put 18 Vals and 6 Zeros against Yorktown and scored 3 hits. The second of 10 Kates and 6 Zeros put 2 torpedoes into Yorktown. This is an excellent result.

F4F did not stop any carrier attack cold in 1942. The combination of poor fighter direction coupled with the sluggish climb of the F4F prevented it.

 

[SaparotRob]

There was only one Japanese wave at Coral Sea and that was very successful. Two torpedoes into Lexington, two bombs into Lexington and one bomb into Yorktown. Lexington sustained several near misses. Yorktown also sustained several near misses, two of which were particularly damaging.
From Lundstrom "First Team": "Thus the combat air and anti-torpedo-plane patrols destroyed three of the eighteen Japanese carrier attack planes. Antiaircraft fire would have to do the rest."
For the dive bomber attack on Lexington, he writes: "The Japanese escort had soaked up the attention of the interceptors and cleared the way for the dive bombers to approach the task force without interference." "Undisturbed by enemy fighters the nineteen Shokaku carrier bombers deployed into a long string in final preparation for their dives."
For the dive bomber attack on Yorktown, he writes: "At 1124, the first Zuikaku kanbaku peeled off to dive. Meanwhile McCormack and Haas just had passed 13,000 feet when they spotted below and slightly ahead the long string of enemy dive bombers waiting their turn to attack." "Although the Zuikaku carrier bombers did not lose any of their numbers to fighter attack, McCormack's ambush certainly did not help their accuracy against the Yorktown." " They claimed between eight and ten hits on a Yorktown-type carrier", but actually got only one, because of the crosswind dives, Buckmaster's skillful ship handling and section "Wildcat Brown.""
At Midway the Hiyru managed to launch two waves. The first put 18 Vals and 6 Zeros against Yorktown and scored 3 hits. The second of 10 Kates and 6 Zeros put 2 torpedoes into Yorktown. This is an excellent result.

F4F did not stop any carrier attack cold in 1942. The combination of poor fighter direction coupled with the sluggish climb of the F4F prevented it.

This event happened before the battle of the Coral Sea.

 

[RCAFson]

The USN studied the effectiveness of its AA fire. It was mid-1944 however before the 5"/38 exceeded the performance of the 20mm in terms of aircraft shot down. Something no doubt helped by the increasing availibility of the VT fuse.

Of course these were wartime studies based upon USN AA kill claims, which we now know to have been greatly overestimated. Long range 5in AA was particularly prone to overclaiming because there would often be multiple ships firing at the same formation, hence multiple claims per actual kill and the USN was not properly vetting accepted claims. In some cases accepted AA kill claims exceeded the number of observed targets despite numerous claims against the same targets by USN CAP.

 

[Shortround6]

The USN studied the effectiveness of its AA fire. It was mid-1944 however before the 5"/38 exceeded the performance of the 20mm in terms of aircraft shot down. Something no doubt helped by the increasing availibility of the VT fuse.

and to show how fast things changed the 20mm was considered by many in late 1944/45 to a warning system to alert the crew to take cover.

We are however looking at several different things.
One was the difference between destroying attacking aircraft and disrupting their attack/aim/effectiveness.
Not the same thing. Land defenses spent a lot of time/effort/money on barrage balloons and smoke generators to decrease effectiveness of enemy attacks even though they destroyed very, very few attacking aircraft.

An AA system can be considered to have worked on a given day if the enemy scored 100% misses even if the AA system shot down 0% enemy aircraft.

Things did change over the years. German with their remote control bombs for one. The Japanese with the Kamikaze also changed things considerably. Just shooting the enemy plane down was no longer good enough. The incoming plane had to be destroyed in flight at sufficient distance to miss the target ship. This is where the 20mm came up short. The 20mms could shoot the incoming target down, but at ranges that allowed the crashing plane (or major parts of it) to hit the ship. Put the 2 together and the US was working on guided missiles and on 3in guns that would fire at 40 to 50 rpm firing proximity fused ammunition. And the radars/fire control to go with them.
The first auto loading 3in gun was test fired on Sept 1st 1945 and the 3in proximity fused ammo was in production for the manual guns.
I am mixing up prototype and first shipboard use but it was only 6 years from the first 1.1 gun going aboard ship to the 3in/50 auto loader test firing so the changes were quick in coming which makes it hard to generalize.

 

[EwenS]

Of course these were wartime studies based upon USN AA kill claims, which we now know to have been greatly overestimated. Long range 5in AA was particularly prone to overclaiming because there would often be multiple ships firing at the same formation, hence multiple claims per actual kill and the USN was not properly vetting accepted claims. In some cases accepted AA kill claims exceeded the number of observed targets despite numerous claims against the same targets by USN CAP.

Yes there was overclaiming, but that was something that the USN was well aware of at the time that these reports were being drawn up and sought to adjust for. Friedman notes:-

"These claims were always optimistic, but the increase suggested the increasing importance of anti-aircraft firepower to the fleet. Analysis suggested that during the third six-month period of the war claims of 'sures' had been overstated by 55 per cent due to duplication....."

 

[Thumpalumpacus]

The SBDs certainly wiped out the Kido Butai's aircraft and that's about, say four hundred aircraft or so? If my suspect memory is right, most of the aircrews were rescued. I think I read that in Shattered Sword.
The aircrews lost to the F4Fs over the sea or jungle were lost with their machines as well.

The Japanese brought about 250 airplanes on the carriers at Midway.

 

[RCAFson]

"In 1931 there was a major review of anti-aircraft defense by the Naval Anti-Aircraft Gunnery Committee. This Committee reaffirmed that the primary method of air attack against ships would be by high level bombers and concluded that destroyers 'are not likely to be the object of high level bombing or torpedo attack' and that dive bombing was not likely to be much of a threat. These conclusions were supported by the RAF, whose thinking in 1931 was that dive-bombing was difficult with any but purpose-built aircraft and concluded that this meant that such single-purpose aircraft were unlikely to be used in large numbers.1"

"1. This thinking was not as wrong-headed as it may appear with twenty-twenty hindsight. To put this in the proper perspective of the time; since 1924 the USN had been developing dive bombing as a means of supporting Marine landing operations. This was mainly performed by fighter planes carrying only small bombs, which was correctly seen by the RAF as not being much of a threat to a warship. However, in 1930, the USN tested dive bombers which were capable of carrying a 1,000 lb. (454 kg) bomb, large enough to sink a destroyer and badly damage larger ships. In May of 1931, the USN started purchasing quantities of the Martin BM-series of dive bombers which could carry a 1,000 lb. (454 kg) bomb for about 400 nautical miles. A total of 32 of these planes had been delivered for service use by June 1933. This was enough planes to equip a squadron, Bombing One (VB-1), which was assigned to USS Lexington (CV-2). Not long after this time the German Luftwaffe recognized the potential of dive bombers and started large-scale procurement of these planes. The Japanese followed, beginning development of what would become their highly effective Aichi D3A "Val" dive bomber in 1936. So, although the RAF was partially correct in its 1931 assessment of dive bombers, it badly misread their future employment."

History and Technology - The British High Angle Control System (HACS) - NavWeaps Anyone with any interest in this topic should read this article and the two others from NavWeaps that make up a set.

So, blaming the RAF isn't really accurate. The Royal Navy made essential decisions at just the wrong moment. By January 1939 the Royal Navy was very aware of the problem (see the footnotes in the article).

The of the set consists of:
HACS: A Debacle or Just-in-Time?
From Fellside to Flyplane
USN Anti-Aircraft Fire Control Comparison

All WW2 long range AA fire control, including the USN's, worked on the principle of engaging targets flying a straight line course. Once a target departs straight line flying, it was nearly impossible for any WW2 AA FC system to bring it down. The only antidote to the dive bomber, other than fighters, was massed automatic cannon. The RN saved weight by using lightweight AA FCS and put the weight saved into providing more 4.7in guns and an autocannon battery. So we have the Tribal and JKN class destroyers armed with 8 or 6 x 4.7in guns, all with AA FC and on mount fuze setters along with a quad 40mm pom-pom and 8 (2 quad) .5in MGs. Even the Hunt class destroyer escorts had 4 or 6 x 4in guns and a quad pom-pom The 40deg elevation of the 4.7in twin mount was sufficient to engage bomber formations coming in under 12000ft, or so and could place a barrage over ships being attacked by dive bombers. Dive bombers would be engaged by the close range autocannon once they ceased formation flying, during their dive attacks.

The biggest problem with the articles linked above is that they all assume that 5in USN tachymetric AA FC was effective, but the data from Lundstrom shows clearly that it was not effective and probably no better than what the RN was using despite it's extra weight and cost. During WW2 the RN seems to have vetted AA kill claims more carefully than the USN but this was probably not known at the time, so USN FC seemed better because they had so many accepted AA kill claims.

 

[RCAFson]

Yes there was overclaiming, but that was something that the USN was well aware of at the time that these reports were being drawn up and sought to adjust for. Friedman notes:-

"These claims were always optimistic, but the increase suggested the increasing importance of anti-aircraft firepower to the fleet. Analysis suggested that during the third six-month period of the war claims of 'sures' had been overstated by 55 per cent due to duplication....."

Yes, and since the USN was overclaiming by a factor of 6 or more in 1942, according to Lundstrom, and the first two USN AA studies published in 1942 (220 AA accepted kill claims at Coral Sea (carriers) Midway, Eastern Solomons, and Santa Cruz vs 35 via Lundstrom's analysis) , even a 55% reduction still greatly overestimated 5In AA performance.

 

[Thumpalumpacus]

There was only one Japanese wave at Coral Sea and that was very successful. Two torpedoes into Lexington, two bombs into Lexington and one bomb into Yorktown. Lexington sustained several near misses. Yorktown also sustained several near misses, two of which were particularly damaging.
From Lundstrom "First Team": "Thus the combat air and anti-torpedo-plane patrols destroyed three of the eighteen Japanese carrier attack planes. Antiaircraft fire would have to do the rest."
For the dive bomber attack on Lexington, he writes: "The Japanese escort had soaked up the attention of the interceptors and cleared the way for the dive bombers to approach the task force without interference." "Undisturbed by enemy fighters the nineteen Shokaku carrier bombers deployed into a long string in final preparation for their dives."
For the dive bomber attack on Yorktown, he writes: "At 1124, the first Zuikaku kanbaku peeled off to dive. Meanwhile McCormack and Haas just had passed 13,000 feet when they spotted below and slightly ahead the long string of enemy dive bombers waiting their turn to attack." "Although the Zuikaku carrier bombers did not lose any of their numbers to fighter attack, McCormack's ambush certainly did not help their accuracy against the Yorktown." " They claimed between eight and ten hits on a Yorktown-type carrier", but actually got only one, because of the crosswind dives, Buckmaster's skillful ship handling and section "Wildcat Brown.""
At Midway the Hiyru managed to launch two waves. The first put 18 Vals and 6 Zeros against Yorktown and scored 3 hits. The second of 10 Kates and 6 Zeros put 2 torpedoes into Yorktown. This is an excellent result.

F4F did not stop any carrier attack cold in 1942. The combination of poor fighter direction coupled with the sluggish climb of the F4F prevented it.

I believe SaparotRob is referring to the action in which O'Hare earned his CMH, in Feb 42. Granted that the attack was land-based, the second wave of it was disrupted by O'Hare and his wingman. Of the nine G4Ms in this wave, only four lined up on Lex and dropped -- scoring no hits.

 

[Reluctant Poster]

It seems like there was some kind of bureaucratic disconnect between the RN, FAA, RAF, and the various aircraft manufacturers. Clearly FAA saw the need for dive bombing, Swordfish, Albacore and Skua had the capability to do it, and did in action, and the later Barracuda could do it as well at least in theory.

There was some kind of problem though, and I suspect it was on the level of specs or requirements more than the manufacturers, but they did not produce the aircraft that they really needed in terms of capabilities and performance. And that is indeed odd when you consider the RAF had the Spitfire, the Mosquito, and the Beaufighter.

I have read about it a bit but after a while the names of all the departments and military acronyms and various Lords and peers of the realm gets a bit confusing. Something about battleship commanders being put in charge of the air arm at the last minute or something?

The Barracuda put a 1600 lb AP bomb into the Tirpitz so it did so in practice as well as theory. Unfortunately to poor quality control (American I might add) it failed to explode and in any event was only half filled with explosive.

 

[Shortround6]

failure to explode seems to have been endemic to AP bombs and shells.

It is a pretty tough situation. You want the projectile (bomb or shell) to smash against a number of inches of armor plate. Punch it's way through and had a fuse that functions to within thousands of a second to explode the main charge. This assumes the fuse is still part of the projectile after making through the armor

The 12,000lb tall boys had a pretty high failure rate as did the 22,000lb bomb. The British 2000lb AP bomb failed around 20% if the time?
British had worked on their AP shells after Jutland.
Part of the problem was testing. In real life the projectiles didn't hit like the test ranges assumed. They hit something small on the way in and they tipped or yawed before penetrating.
They often still penetrated but the forces from the sort of sideways hit distorted the projectile body and knocked the fuse loose (ejected it).

I do find the store about the American AP bomb being 1/2 filled a little doubtful.
Very poor quality control on the Americans. You would have thought they weighed them before and after filling for instance.
The bombs are not shipped/transported with fuses in place so unless there was a large hidden cavity in the explosive filler one would think that the a larger than normal cavity would have alerted somebody along the way (they are shipped with transit plugs which are removed before fuse/s are fitted.
Not saying the Americans couldn't screw up but that seems to have been multiple screw ups.

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3 Description The bodies are of single piece, forged, machined construction, with pointed noses, parallel sides, and slight boat tailing. The

bulletpicker.com

 

[Reluctant Poster]

I believe SaparotRob is referring to the action in which O'Hare earned his CMH, in Feb 42. Granted that the attack was land-based, the second wave of it was disrupted by O'Hare and his wingman. Of the nine G4Ms in this wave, only four lined up on Lex and dropped.

1. He did specify Coral Sea.
2. I reviewed the Feb 20 attack and I disagree that the Beattys were stopped "stone cold". Four bombers out of nine in the first wave and four bombers out of eight in the second wave completed their bombing runs. The fact that they caused no damage was due to the bombing method. Level bombing never worked on warships in the open sea.

 

[SaparotRob]

I have always been amazed that ordnance doesn't either explode in the gun tubes when fired or just blow up upon hitting anything when dropped. That's some serious kinetic energy.

 

[RCAFson]

I believe SaparotRob is referring to the action in which O'Hare earned his CMH, in Feb 42. Granted that the attack was land-based, the second wave of it was disrupted by O'Hare and his wingman. Of the nine G4Ms in this wave, only four lined up on Lex and dropped -- scoring no hits.

The battle off Bougainville (Feb 20 1942) is a particularly interesting one, in terms of looking at USN 5in AA performance. USN CAP reported the 5in AA fire from the USN TF was almost completely ineffective, and Lundstrom notes only two IJN bombers were damaged and/or downed by close range AA but only after the bombers had been damaged by CAP, yet the USN awarded 6 confirmed AA kills. The USN CAP made 15 kill claims and SBDs several more, so against 17 bombers the USN awarded 6 AA kills, despite ~17 CAP kill claims!

 

[EwenS]

I do find the store about the American AP bomb being 1/2 filled a little doubtful.
Very poor quality control on the Americans. You would have thought they weighed them before and after filling for instance.
The bombs are not shipped/transported with fuses in place so unless there was a large hidden cavity in the explosive filler one would think that the a larger than normal cavity would have alerted somebody along the way (they are shipped with transit plugs which are removed before fuse/s are fitted.
Not saying the Americans couldn't screw up but that seems to have been multiple screw ups.

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3 Description The bodies are of single piece, forged, machined construction, with pointed noses, parallel sides, and slight boat tailing. The

bulletpicker.com

The story about the bomb being half filled originates from the Germans that disarmed it.

"The other hit was to prove to be the Fleet Air Arm's greatest disappointment. A 726 kg (1,600 lb) AP bomb hit just forward of the bridge on the port side and penetrated not only the upper deck but the armoured deck below, finally coming to rest in No. 4 Switch Room on the lower platform deck, having gone through 14,6 cm (5¾ inches) of decking, mostly armoured steel. It failed to explode and when the Germans finally removed the explosive there was only 45 kg (100 lb) instead of 98 kg (215 lb). Had this bomb exploded it would have wrecked the main fire control room and the switchboard room as well as causing serious flooding. Of this attack the German records state:



"The attack on 24 August 1944 was undoubtedly the heaviest and most determined so far. The English showed great skill and dexterity in flying. For the first time they dived with heavy bombs. During the dive bombing, fighter planes attacked the land batteries which, in comparison with earlier attacks, suffered heavy losses. The fact that an armour-piercing bomb of more than 699 kg (1,540 lb) did not explode must be considered an exceptional stroke of luck, as the effects of that explosion would have been immeasurable. Even incomplete smoke screening upsets the correctness of the enemy's aim and it has been decided from now on to use it in wind strengths up to 9 meters/second (8.2 yards/second) irrespective of possible gaps"."

Bismarck-Class

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3 Description The bodies are of single piece, forged, machined construction, with pointed noses, parallel sides, and slight boat tailing. The

bulletpicker.com

 

[Thumpalumpacus]

1. He did specify Coral Sea.
2. I reviewed the Feb 20 attack and I disagree that the Beattys were stopped "stone cold". Four bombers out of nine in the first wave and four bombers out of eight in the second wave completed their bombing runs. The fact that they caused no damage was due to the bombing method. Level bombing never worked on warships in the open sea.

No, he only mentioned Lexington initially, and then later clarified that it was before Coral Sea.

I'm aware that that attack wasn't "stopped cold", which is why I posted numbers showing that. I only mentioned it because I though that might be the attack Rob was thinking of -- which seems to be the case, even if he didn't remember it so clearly. Shit, I'd forget my butt if it wasn't stuck on my back.

Anyway, hope that helps.

 

[Shortround6]

Thank you.

Very poor quality control.

 

[Reluctant Poster]

The story about the bomb being half filled originates from the Germans that disarmed it.

"The other hit was to prove to be the Fleet Air Arm's greatest disappointment. A 726 kg (1,600 lb) AP bomb hit just forward of the bridge on the port side and penetrated not only the upper deck but the armoured deck below, finally coming to rest in No. 4 Switch Room on the lower platform deck, having gone through 14,6 cm (5¾ inches) of decking, mostly armoured steel. It failed to explode and when the Germans finally removed the explosive there was only 45 kg (100 lb) instead of 98 kg (215 lb). Had this bomb exploded it would have wrecked the main fire control room and the switchboard room as well as causing serious flooding. Of this attack the German records state:



"The attack on 24 August 1944 was undoubtedly the heaviest and most determined so far. The English showed great skill and dexterity in flying. For the first time they dived with heavy bombs. During the dive bombing, fighter planes attacked the land batteries which, in comparison with earlier attacks, suffered heavy losses. The fact that an armour-piercing bomb of more than 699 kg (1,540 lb) did not explode must be considered an exceptional stroke of luck, as the effects of that explosion would have been immeasurable. Even incomplete smoke screening upsets the correctness of the enemy's aim and it has been decided from now on to use it in wind strengths up to 9 meters/second (8.2 yards/second) irrespective of possible gaps"."

Bismarck-Class

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3

Bomb, 1600 lb AP, AN-Mk 1 Mod 1, 2, 3 Description The bodies are of single piece, forged, machined construction, with pointed noses, parallel sides, and slight boat tailing. The

bulletpicker.com

I found this comprehensive report on the damage suffered by the Tirpitz from the various attacks on her throughout the war.

https://www.navy.gov.au/sites/default/files/documents/Battle_Summary_Tirpitz_Vol_2.pdf