How Accurate Was Dive Bombing

[yosimitesam]

Suppose you have a reasonably competent pilot, with reasonable hardware, on a reasonable day, an no one shooting at him (so maybe in training). How accurate was dive bombing? How likely would it be to hit a ship, or a pill box?

Here's some info where F4U's and SBD's were compared as dive bombers against land targets. The F4U lowered its landing gear for dive brakes. Apparently the F4U's landing gear was designed to take the stresses, as the usual 'max speed with gear down' restrictions didn't apply.

 

[pbehn]

Here's some info where F4U's and SBD's were compared as dive bombers against land targets. The F4U lowered its landing gear for dive brakes. Apparently the F4U's landing gear was designed to take the stresses, as the usual 'max speed with gear down' restrictions didn't apply.

View attachment 621364

Hate to be a pedant but doubling the diameter/radius doesnt double the size of the target. 50x50=2,500 100x100= 10,000, it just doubles the distance from the aim point the area is 4 times bigger.

 

[yosimitesam]

Hate to be a pedant but doubling the diameter/radius doesnt double the size of the target. 50x50=2,500 100x100= 10,000, it just doubles the distance from the aim point the area is 4 times bigger.

The military generally "measures" bombing error by angles (mils) rather than by linear distance, so doubling the radius will double the multiplier of the tangent of the error-angle. Rather than seeing the situation as dropping particles randomly in a circle of a certain size (as in classical probability theory), they see the error as the bombing angle being off (due to pilot error) by so many mils, which is proportional to the radius which equals the height x tan(bomb-angle). So the writer should have written something like "doubling the allowed angle error triples the number of hits." As an example, I recently read an article about the post-war APQ-23 bombing radar system that said something like "its theoretical accuracy was 0.18 mils but its practical accuracy was 0.25 mils." So the actual linear ground error was height x tan(0.25mils), for any height, which means you don't generally have to state what the height is to get a measure of the system's overall accuracy. This is probably what the writer meant but his editor didn't catch it.

 

[Koopernic]

The German shipborne radars used a fairly narrow beam radar and would have to have the receiver/transmitter aimed at the aircraft in order to detect it. There is no evidence via Tirpitz's War Diary (March 1942) that she was able to detect aircraft at long range via radar.

Seetakt was detecting aircraft from its inception, in 1935. Both a Freya radar and a Seetakt radar (at the German naval station at Whilhemshaffen) detected an inbound raid of Wellingtons that was almost completely destryed by Me 109 interceptors. The two radar operators contacted each other. A Beam width of 6 degrees is adequate for detecting aircraft.

On the day of operation Catechism, the Lancaster bomber raid that sank Battleship Tirpitz the ships radar detected the Lancaster's at 150km range (see Niklas Zetterling book on Tirpitz) and provided Tirpitz's first warning.

Tirptiz was sunk because the Luftwaffe did not intercept due to a a combination of bad luck, Ju 52 landing on the fighters runway and likely espionage at the Luftwaffe's Wassermann radar station.

By 1942 Kreigsmarine u-boats were getting FuMO 61 Hohtenweil radars which had a mattress aerial in the side of the conning tower, in 1943 small ships received it and latter in the year Hohtenweil received a full PPI (Plan Position Indicator) referred to as a panorama display. Tirpitz received a hohtenweil as did Prinz Eugen.

In 1944 some ships (torpedo boats) and larger units such as Bismark and also Prinz Eugen also received FuMo 81 Berlin 9cm microwave radars.

Whatever is in the war diary would be cryptic as radar would only be referred to peripherally, likely as EM-2 (range finder 2,the code word for radar on German ships) and in any case German navy tended to maintain radio and radar silence.

 

[Koopernic]

The Japanese magnetron was not the same design as the cavity magnetron developed by the UK (Randall and Boot) and was never capable of generating high power output.

The Japanese magnetron worked in exactly the same way: circular cavities with narrow slits. The Japanese even developed strapping. The difference was that the British magnetron was machined out of a solid copper block with water cooling into the main copper whereas the Japanese magnetron was fabricated and installed in a glass case to maintain vacuum and lacked water cooling. There are pictures around and I have a $500/book folly published by the IEEE.

The Japanese type 22 radar had the same range, about 24km which they achieved by using a long pulse of about 10 micro seconds leading to an range accuracy of about 300m.

The Japanese did develop more powerful magnetrons including water cooling (in development). They also introduced lobe switching using 3 horn antenna (central transmit, left and right receive) .

There are a lot of radar myths out there.

If there had of been fortnightly curior flights between German and Japan its likely the Germans would have become aware of the Japanese microwave radar and it would have helped them immensely.

 

[RCAFson]

Seetakt was detecting aircraft from its inception, in 1935. Both a Freya radar and a Seetakt radar (at the German naval station at Whilhemshaffen) detected an inbound raid of Wellingtons that was almost completely destryed by Me 109 interceptors. The two radar operators contacted each other. A Beam width of 6 degrees is adequate for detecting aircraft.

On the day of operation Catechism, the Lancaster bomber raid that sank Battleship Tirpitz the ships radar detected the Lancaster's at 150km range (see Niklas Zetterling book on Tirpitz) and provided Tirpitz's first warning.

Tirptiz was sunk because the Luftwaffe did not intercept due to a a combination of bad luck, Ju 52 landing on the fighters runway and likely espionage at the Luftwaffe's Wassermann radar station.

By 1942 Kreigsmarine u-boats were getting FuMO 61 Hohtenweil radars which had a mattress aerial in the side of the conning tower, in 1943 small ships received it and latter in the year Hohtenweil received a full PPI (Plan Position Indicator) referred to as a panorama display. Tirpitz received a hohtenweil as did Prinz Eugen.

In 1944 some ships (torpedo boats) and larger units such as Bismark and also Prinz Eugen also received FuMo 81 Berlin 9cm microwave radars.

Whatever is in the war diary would be cryptic as radar would only be referred to peripherally, likely as EM-2 (range finder 2,the code word for radar on German ships) and in any case German navy tended to maintain radio and radar silence.

Tirpitz's War Diary makes no mention of radar detection of aircraft.

What shore based radar could do is not really relevant. KM shipborne radar was broadly equivalent to RN Type 284. Yes, type 284 could detect aircraft, but is was terribly inefficient at it because of the narrow radar beam which meant that the director upon which it was mounted would have to be rotating constantly to scan the horizon. Tirpitz, by 1944 was a static shore battery and was given, the equivalent to a shore based radar installation. RN type 79 was operational in 1938 and was a dedicated long range AW radar. Type 279, was similar but had a FC ranging unit added to it. It was used operationally from 1940.

 

[RCAFson]

The Japanese magnetron worked in exactly the same way: circular cavities with round slits. The Japanese even developed strapping. The difference was that the British magnetron was machined out of a solid copper block with water cooling into the main copper whereas the Japanese magnetron was fabricated and installed in a glass case to maintain vacuum and lacked water cooling. There are pictures around and I have a $500/book folly published by the IEEE.

The Japanese type 22 radar had the same range, about 24km which they achieved by using a long pulse of about 10 micro seconds leading to an range accuracy of about 300m.

The Japanese did develop more powerful magnetrons including water cooling (in development). They also introduced lobe switching using 3 horn antenna (central transmit, left and right receive) .

There are a lot of radar myths out there.

If there had of been fortnightly curior flights between German and Japan its likely the Germans would have become aware of the Japanese microwave radar and it would have helped them immensely.

As you state the UK magnetron was a very different design. RN Type 271/273 had a much longer range due to the higher power output, and range was essentially horizon limited. Duke of York's Type 273 detected Scharnhorst at ~41km, when only her upper superstructure was above the horizon. The IJN Type 22 vastly inferior.

 

[tomo pauk]

This is what P-47 was capable for (from the docs hosted on this site; click on the thumbnail):

 

[Koopernic]

As you state the UK magnetron was a very different design. RN Type 271/273 had a much longer range due to the higher power output, and range was essentially horizon limited. Duke of York's Type 273 detected Scharnhorst at ~41km, when only her upper superstructure was above the horizon. The IJN Type 22 vastly inferior.

No, the UK magnetron didn't work in different ways. It used circular cavities and narrow slits. The physics was the same. It had water cooling and was solid copper that is what allowed it to operate at much higher power levels. Dr S.Nakajima who headed JRC (Japanese Radio Company) department that developed these radars amongh other complained in the IEEE book "Radar Development to 1945" that he started the war with a workforce of 800 and ended it with 400. He said "The Japanese military had no basic policy in drafting personnel" and that many ended up as foot soldiers. This is what stopped them refining their product. The Japanese did develop type 32 which offered 35km range (essentially to the horizon) and had lobe switching for blind fire control. It still used the 2kW magnetron. It was simply physically larger antenna. Dr Nakajima said JRC had a solid metal water cooled magnetron ready in 1945 but said "we couldn't move on it because there was no allocation of materials for it. From the first radar to the last the Japanese military didn't allocate the nickel for the magnets or the copper for the magnetrons. They also had PPI. The Japanese radar also functioned as a radar detector with the transmitter switched off.

UK type 284 radar was originally 25kW and rather unreliable due to requiring a 20 minute warmup time and a shutdown after a few hours. The Germans had non of these problems and their 1.5kW and 8kW radar had the same range. As continuous use was possible there was no problem with using them as search radars for aircraft and surface search. The Seetakts used grid modulation and a longer pulse to get the range but recovered accuracy from the greater precision of the grid modulation circuit and phase recovery. The UK radars overcame these latter problems and Type 284M and Type 284P started appearing around 1942 with 125kW pulse and lobe switching to allow blind fire.

The Seetakt received a 125kW modulator in 1942 as well but only on land based "Calais" versions. This is because Seetakt up until then had used grid modulation to turn the pulse on and off as well as generate the wave whereas the British radar used anode modulation in which the grid generated the wave but the pulse was created by pulsing the whole valve like a spark plug. Hence the Germans tried this first on land based installations due to the high voltages required and planed a latter installation at sea.

When Scharnhorst encountered Burnetts three cruisers and then Duke of York (DoY) during the Battle of North cape it was very bad timing for the Germans as Scharnhorst just missed out on radar upgrades that were a few months away at most.

1 Firstly note that the Germans were outnumbered and had to observe radio silence whereas the British being the superior force could keep their radars on.
2 In All encounters German passive radars (or infrared) detected the British radar (both the cruisers and Duke of York) and gave sufficient warning for the German crews to at least get to action stations and start the process of getting their guns pointing in the correct direction. The German microwave warning device Naxos was also unreliable at this time.

3 The forward facing Seetakt was damaged in the encounter with the cruisers but the rear radar was working. It could detect the British ships and direct fire against them but at the great ranges involved the German radar could not see the shell splash and correct aim whereas the British with their bigger shells and more powerful radar could (although Scharnhorst pulled away and got out of shell splash radar range when a lucky shot ( moments before DoY was about to give up) hit a shot trap near her engine room and slowed her down.

4 The emphasis for the German navy was improving radar on its u-boats. The three capital ships the
Tir[pitz, Scharnhorst and Prinz Eugen had to wait. Scharnhorst thus missed out on the Backup Hohtenweil PPI radar being fitted in 1943 to u-boats and torpedo boats latter fitted to Prinz Eugen and Tirptiz as well as the FuMO 81 microwave surface search radar towards the end of 1944.

5 The 8kW 24km range FuMO 26 was supposed to be replaced by the 125kW FuMO 34 which could detect to the radar horizon and sport shell splash to it (due to its long shaped pulse). It seems Tirpitz had a 125kW pulse as a 'one off' since it could detect the incoming Lancaster raid at 150km.


Hence those imagining Bismarck battling a KGV or Iowa class in late 1944 or early 1945 should consider with a late war fitout more or less matched them or nearly so. (Iowa's 1945 fitout is pretty impressive because its radar could spot shell splash over the visual horizon not only for range but bearing deviation)

Tirpitz's War Diary makes no mention of radar detection of aircraft.

What shore based radar could do is not really relevant. KM shipborne radar was broadly equivalent to RN Type 284. Yes, type 284 could detect aircraft, but is was terribly inefficient at it because of the narrow radar beam which meant that the director upon which it was mounted would have to be rotating constantly to scan the horizon. Tirpitz, by 1944 was a static shore battery and was given, the equivalent to a shore based radar installation. RN type 79 was operational in 1938 and was a dedicated long range AW radar. Type 279, was similar but had a FC ranging unit added to it. It was used operationally from 1940.

Seetakt was modified to both have a surface search, support air search, anti aircraft fire control and blind fire ability with multi role antena.

Type 79 and Type 279 were long wave radars that could not detect a surface submarined or a periscope nor could they be fitted to smaller ships. This made British convoy escorts fairly ineffective at the start of the war. Seetakt could do all of this and on a 1000 ton torpedo boat. It may not have been the best air warning radar but it did perform that job effectively. As I have pointed out the Krieksmarine supplmented its radars with a Hohtenweil PPI type from 1943-1944 and with a microwave type called FuMO 81 from late 1944 onwards.

 

[Koopernic]

I had read somewhere that a stuka could usually get its bombs within 20m but it should be noted that the early Ju 87 didn't have the StuVi 5B whivh did some primitive calculations to compensate for dive speed.

Unless a dive bombing attack was 90 degrees vertical the method was to determine a dive angle and release height and consult tables to establish the dive speed and the bomb trail error. The bomb sight was then fore sighted to take into account the bomb trail error. In the Ju 87 a contact altimeter sounded a siren 250m before the release point, when it stopped it was time to release. Pullup was automatic and occurred upon bomb release. The procedure was much the same in the US bombers. I think the Ju 87 tended to do vertical dives for which no fore sighting for bomb trail error is required but the USN preferred a non vertical dive since it was easier to follow a ship this way., If you aimed for the middle of the ship and the bombs were a little short or far it didn't matter on a 160m long ship.

Latter Ju 87 had the StuVi 5B which carried out primitive corrections and moved the reticule. However the StuVi 5B worked best with the BZA computer (used on Ju 88, Me 410, Ar 234) which calculated the point continuously using gyros and other sensor and gave a continuous impact point into the StuVi 5B.

I know US naval dive bombers had some computing sight that included the use of a radar altimeter.

At the end of the war both USN and Luftwaffe were trialling toss bombing sights.

A dive bomber was a very difficult target for the ship defending itself due to its small frontal area.

On land ever a distant 40mm Boffors gun with a director could predict the dive bombers trajectory but it was much harder if only the small area of the dive bomber was seen.

This is why US dive bombers used as vertical an attack as possible against Yamato.

 

[yosimitesam]

At the end of the war both USN and Luftwaffe were trialling toss bombing sights.

The US Navy's was called ASG-10 or "Bomb Director Mark 1" and wasn't as sophisticated as the German's. The ASG-10 calculated release using the angle of attack plus the DELTA (difference) in barometric altitude between 2 (of several) set heights. Using the difference in barometric altitude (rather than an absolute altitude via radio altimeter) was technically 'easier'. I posted the manual (dated 1945) for the ASG-10 on this site (link below.) It is clever in the way it worked. Its design was probably mandated to be 'simple as possible' to allow 'toss bombing', i.e shallower dives directly at the target and using the measured pull up g-forces to give the bomb a slight 'toss' upward to compensate for trail (gravity). A continuous system (allowing release from any altitude) would be far more complicated but definitely the way to go, as soon as better electronics (1950's) would allow.

ASG-10 Manual

 

[RCAFson]

No, the UK magnetron didn't work in different ways. It used circular cavities and narrow slits. The physics was the same. It had water cooling and was solid copper that is what allowed it to operate at much higher power levels. Dr S.Nakajima who headed JRC (Japanese Radio Company) department that developed these radars amongh other complained in the IEEE book "Radar Development to 1945" that he started the war with a workforce of 800 and ended it with 400. He said "The Japanese military had no basic policy in drafting personnel" and that many ended up as foot soldiers. This is what stopped them refining their product. The Japanese did develop type 32 which offered 35km range (essentially to the horizon) and had lobe switching for blind fire control. It still used the 2kW magnetron. It was simply physically larger antenna. Dr Nakajima said JRC had a solid metal water cooled magnetron ready in 1945 but said "we couldn't move on it because there was no allocation of materials for it. From the first radar to the last the Japanese military didn't allocate the nickel for the magnets or the copper for the magnetrons. They also had PPI. The Japanese radar also functioned as a radar detector with the transmitter switched off.

UK type 284 radar was originally 25kW and rather unreliable due to requiring a 20 minute warmup time and a shutdown after a few hours. The Germans had non of these problems and their 1.5kW and 8kW radar had the same range. As continuous use was possible there was no problem with using them as search radars for aircraft and surface search. The Seetakts used grid modulation and a longer pulse to get the range but recovered accuracy from the greater precision of the grid modulation circuit and phase recovery. The UK radars overcame these latter problems and Type 284M and Type 284P started appearing around 1942 with 125kW pulse and lobe switching to allow blind fire.

The Seetakt received a 125kW modulator in 1942 as well but only on land based "Calais" versions. This is because Seetakt up until then had used grid modulation to turn the pulse on and off as well as generate the wave whereas the British radar used anode modulation in which the grid generated the wave but the pulse was created by pulsing the whole valve like a spark plug. Hence the Germans tried this first on land based installations due to the high voltages required and planed a latter installation at sea.

When Scharnhorst encountered Burnetts three cruisers and then Duke of York (DoY) during the Battle of North cape it was very bad timing for the Germans as Scharnhorst just missed out on radar upgrades that were a few months away at most.

1 Firstly note that the Germans were outnumbered and had to observe radio silence whereas the British being the superior force could keep their radars on.
2 In All encounters German passive radars (or infrared) detected the British radar (both the cruisers and Duke of York) and gave sufficient warning for the German crews to at least get to action stations and start the process of getting their guns pointing in the correct direction. The German microwave warning device Naxos was also unreliable at this time.

3 The forward facing Seetakt was damaged in the encounter with the cruisers but the rear radar was working. It could detect the British ships and direct fire against them but at the great ranges involved the German radar could not see the shell splash and correct aim whereas the British with their bigger shells and more powerful radar could (although Scharnhorst pulled away and got out of shell splash radar range when a lucky shot ( moments before DoY was about to give up) hit a shot trap near her engine room and slowed her down.

4 The emphasis for the German navy was improving radar on its u-boats. The three capital ships the
Tir[pitz, Scharnhorst and Prinz Eugen had to wait. Scharnhorst thus missed out on the Backup Hohtenweil PPI radar being fitted in 1943 to u-boats and torpedo boats latter fitted to Prinz Eugen and Tirptiz as well as the FuMO 81 microwave surface search radar towards the end of 1944.

5 The 8kW 24km range FuMO 26 was supposed to be replaced by the 125kW FuMO 34 which could detect to the radar horizon and sport shell splash to it (due to its long shaped pulse). It seems Tirpitz had a 125kW pulse as a 'one off' since it could detect the incoming Lancaster raid at 150km.


Hence those imagining Bismarck battling a KGV or Iowa class in late 1944 or early 1945 should consider with a late war fitout more or less matched them or nearly so. (Iowa's 1945 fitout is pretty impressive because its radar could spot shell splash over the visual horizon not only for range but bearing deviation)



Seetakt was modified to both have a surface search, support air search, anti aircraft fire control and blind fire ability with multi role antena.

Type 79 and Type 279 were long wave radars that could not detect a surface submarined or a periscope nor could they be fitted to smaller ships. This made British convoy escorts fairly ineffective at the start of the war. Seetakt could do all of this and on a 1000 ton torpedo boat. It may not have been the best air warning radar but it did perform that job effectively. As I have pointed out the Krieksmarine supplmented its radars with a Hohtenweil PPI type from 1943-1944 and with a microwave type called FuMO 81 from late 1944 onwards.

The UK magnetron was not the same as the IJ magnetron, which had vastly less power output and comparing operational UK radars versus experimental axis radars is not very useful.

Could you point out an example of early war seaborne KM radar detecting aircraft at long range?

Type 271 was developed expressly for small ships and become operation in mid 1941.

 

[VBF-13]

Suppose you have a reasonably competent pilot, with reasonable hardware, on a reasonable day, an no one shooting at him (so maybe in training). How accurate was dive bombing? How likely would it be to hit a ship, or a pill box?

Under those conditions, in an SBD, I'm going with pill box. That's how good that bad boy was. Those cadets were hitting die markers in the Gulf of Mexico, 4 for 5 and 5 for 5. My Dad's docket shows the runs and scores he and his "crew" got. But I heard it in his retiree club, too, and how much the pilots loved that "Speedy D," whether it was the one they ended in, or just trained some in. So, put me down for pill box in the poll.

 

[pops-paolo]

(this is a bit off topic) The one good thing about dive-bombing compared to the torpedo bombing (if you wanna take out a ship) was as a dive bomber you would start at a higher altitude and you would be moving very fast throughout the bombing run while torpedo bombers had to be slow a low to the sea level.

 

[GrauGeist]

Dick Best used the Akagi's Hinomaru (painted on the deck) as his aiming point and missed it by a few feet.
Kleiss missed the Kaga's Hinomaru by about the same margin.

The SBDs that struck the Hiryu also used her Hinomaru as an aim point and photos of the Hiryu after the attack show the forward area where the Hinomaru was, completely blown out.

Plenty more examples, but figure that the Hinomaru painted on Japanese Fleet carriers are about 40 feet wide (not sure, but estimated, as it was a bit wider than the wingspan of the D3A), so roughly the size of a substantial pillbox.

 

[Thumpalumpacus]

(this is a bit off topic) The one good thing about dive-bombing compared to the torpedo bombing (if you wanna take out a ship) was as a dive bomber you would start at a higher altitude and you would be moving very fast throughout the bombing run while torpedo bombers had to be slow a low to the sea level.

Versus carriers, sure -- assuming you caught them at the right time.

 

[GrauGeist]

Versus carriers, sure -- assuming you caught them at the right time.

Although the "very fast" part is not all that true - Stukas, SBDs, A-36s, Vals, etc. all deployed dive-brakes that limited their dive speed.
The SBD's massive dive-brakes held it steady at 250mph in it's 70-80 degree dive.
The Stuka was about 350mph in it's near-vertical dive.
The A-36 Mustang was about 390mph and the D3A 273mph.

 

[Milosh]

AA had a hard time tracking a/c in the vertical compared to the horizontal.

 

[Thumpalumpacus]

Although the "very fast" part is not all that true - Stukas, SBDs, A-36s, Vals, etc. all deployed dive-brakes that limited their dive speed.
The SBD's massive dive-brakes held it steady at 250mph in it's 70-80 degree dive.
The Stuka was about 350mph in it's near-vertical dive.
The A-36 Mustang was about 390mph and the D3A 273mph.

I get what he's saying, though. Torp bombers, flying lower and slower, seem more vulnerable.

Of course a good dive-bomber uses braking for accuracy, but even that is a plus, given that the fighters ostensibly chasing them lack said brakes and dive faster, right?

Torp bombers didn't have that leg-up. They came in low and level on a steady course to aim the missile right.

That's what I think he was trying to say, at least.

 

[A.G. Williams]

At the beginning of WW2 torpedoes had to be dropped at a relatively low speed, but a lot of work was done during the war to increase the permitted water impact speed, so they could be dropped at high aircraft speeds.