Terminal ballistics: ID of WW2 amm holing a Thai bridge


#10

Is there records of who was operating in the area? That would allow to narrow down certain aircraft types.


#11

Jack’s recemmendation is a good one. Beaufighters are a good candidate. They were active in this Theater of Operations. In fact, Graham Irving, who many of you will remember, was an engine mechanic on them in India and other locations in this area.

Cheers,
Lew


#12

The Beaufighter (one of my favourites) was used in many armament configurations - a great machine!

en.wikipedia.org/wiki/Bristol_Beaufighter

Images:
google.de/search?q=beaufigh … 20&bih=933


#13

[color=#008000]Thank you: Beaufighter. Working on that.

Seems 211 Squadron with Beaufighter Xs is the most likely candidate right now. There are also these to go through:

No. 27 (F) Squadron - Beaufighter Vf , then Beaufighter X
No. 89 (F) Squadron - Beaufighter VIf, later Mosquito
No. 176 (F) Squadron - Beaufighter VIf

I’ll brief my results here as they develop and add full commentaries to my website.

Not to forget the P-38s.[/color]


#14

For Point G, with a hole diameter of 60mm, I’m trying to flesh in a hypothesis that an exploding HE shell might have produced a hole larger than the caliber of the shell. It has now been suggested that this explanation might be irrelevant because 20mm HE shells may have had time-delay fuses, that delay being around one millisecond after impact. The delay was intended to allow a shell to penetrate an object before exploding which presumably would then have done more damage. That delay would also have been sufficient for a shell to have exited the built-up structural member entirely to explode harmlessly in an open area of the bridge.

Hence, the question: might WWII-vintage 20mm HE shells, as used in aircraft Hispano cannons, have had time-delay mechanisms?


#15

[quote=“islandee”]

Hence, the question: might WWII-vintage 20mm HE shells, as used in aircraft Hispano cannons, have had time-delay mechanisms?[/quote]
Yes, they did. The original HE shells used in 1941 did not, and were found to be ineffective because the shells exploded on the skin of the aircraft rather than inside it (the Luftwaffe had the same problem). For a while the practice ball rounds were used instead, as they were big enough to penetrate deeply into the structure and do a lot of damage even without chemical contents. These were eventually replaced by HEI shells with delayed-action fuzes.

You should bear in mind that penetrators could punch bigger holes than their own diameters. I have a piece of armour plate with a hole of approx 6mm diameter punched through it by the (saboted) 4mm tungsten bullet from a 6.5x25 CBJ round.


#16

After some interruptions, I’m back to the shell holes in the San Khayom bridge. I apologize for the length of this; but I don’t know how to shorten it further.

With regard to the hole at Point A, I’m trying to visualize the actions of the aircraft that produced the hole. I’d like to include a sketch on my webpage of the possible / probable path of the aircraft during its attack.

The consensus is that the hole is apparently from a 20mm projectile; and in the Southeast Asia Theater both the P-38 and the Bristol Beaufighter carried HS.404 cannon which used that ammunition. I’ll use the P-38 as a subject here simply because I can find more information about it (the Beaufighter might be the better candidate because, beyond its harmonization range, it would have offered a dispersion pattern with its four cannon: such a pattern might more easily have included Point F, the other 20mm impact point on the bridge. [color=#FF0000]Does anyone know of an on-line presentation, including sketches, perhaps a manual, for harmonizing the guns on a Beaufighter?[/color]).

So, scenario: a P-38 pilot happened upon a “target of opportunity”, a train traveling south out of Lamphun and approaching San Khayom bridge. The pilot reduced altitude so as to fire on the train. Coming into range, he fired for a certain period; then he broke contact and climbed away from the train and the bridge.

Angle of attack: The exit angle of Hole A measures about 12° to the horizontal. In the sketch below, I assume the bullet path was almost unaffected in passing through the comparatively thin bridge plate (projectile diameter was twice the thickness of the target plate). On that basis, I assume the pilot dropped to an altitude matching the 12° allowing an angle of attack of 12°.

A P-38’s single 20mm cannon was centrally mounted in the fuselage and its operation was basically point (the plane)-and-shoot. The range of the cannon was limited primarily by the pilot’s visual acuity and his properly adjusting for bullet drop (excluding weather, aircraft performance, pilot skills, whatever).

I assume an attack speed of 350 mph: a P-38’s cruising speed was 275 mph and max speed was 414 mph. A velocity diagram would look like this for a 12° dive at 350 mph:

The important information here is that, flying at a down-angle of 12° and at a speed of 350mph, the aircraft would have been dropping 107 feet per second.

The idealized flight path would have looked like this:

Of course, the pilot would have disengaged at some point before his aircraft flew into the target.

Questions.

[color=#FF0000]Do these assumptions and the scenario seem plausible? If not, I’d appreciate being corrected. [/color]

If the scenario is not too far off:

[ul][color=#FF0000]At what range would the pilot likely have started firing?[/color] (I read that one B-25 gunner had his guns harmonized for 1000 yards: he cautioned that this was useful only for stationary targets)
And [color=#FF0000]at what altitude would the pilot have had to disengage (how much altitude would be burned up after the pilot tried to gain altitude; and how much spare altitude should he have allowed)[/color]?
Tying these down would also establish how long the pilot might have fired.
[/ul]

Alternate scenario: With the above presented, there is a piece of data which could contradict this scenario, and I don’t have the background to interpret it: the “floor” of Hole A is at an angle of about 7° to the horizontal. If 7° (not the 12° used above) were the angle at which the projectile entered the plate, and the exit angle was, as actually measured, 12°, then passing through the plate would have bent the projectile’s course by 12° - 7° = 5° (see cross-section).

If the angle of attack were a very lean 7°, then at a range of 1000 yards, the gun would have been only 366 feet off the ground — with bullet drop compensated for by either, an extra 24 more feet for a total of 390 feet, or a slight tilt upward in angle of attack. And at 500 yards 183 feet (compensated for 4 feet of bullet drop). On the other hand, the aircraft’s altitude loss while changing from a down-angle of 7° to actually moving upward would have been less than recovering from a down-angle of 12°. But operating that close to the ground at 350 mph or more seems unlikely (which is why I didn’t include it in my main presentation above); though I am willing to be corrected.

[color=#FF0000]Are there any comments about this alternative?[/color]


#17

As nobody is answering I will try to add a bit to the questions rather than the answers – sorry for this.
I am not really entitled to state on this but from my limited insight and the few years I spent following my interest on aircraft and aircraft armament I can only suggest a few things. Also I think we have some USAF armorers here and even a pilot with combat experience (Mel Carpenter) who may tell us much more (less on WWII though I think) and if so any of the guys in question please correct what is said below.

Regarding engagement distances, duration of attack and break of contact:
There are several factors which do influence the answer on this.

  1. What kind of target is selected?
  2. Moving or still target?
  3. Daytime and day light situ, dusk, dawn, bright day, opposing sun
  4. Weather in regard to heavy rain (snow we can exclude I guess)
  5. Actual situ in air like enemy planes
  6. Actual situ on ground like was the train close to a densely overgrown area (jungle) or a tunnel ahead?
  7. Is the target actively defended/was the attacking plane fired at?
  8. Ordnance load/configuration of the attacking plane and what ordnance was used on the actual strafing run, if rockets or air dropped ordnance were used in conjunction with the guns a safety distance had to be kept as shrapnel would endanger the attacking plane.
  9. Available amount of ammunition at the moment of engagement, means if the full load out was available or less as prior strafing might have depleted the available amount of ammo and only the last remaining rounds were fired during the strafing run investigated here.

So for a better answer to your question or at least for narrowing it down to fewer possibilities it my be helpfull to try to find the combat reports on the area.

  • Who was flying in the region at the time the incident took place?
  • Then finding the Unit and establishing the aircraft type
  • Trying to find the reports of this unit in archives (or even the Pilot’s name)
  • Finding the actual report for the flight in question

As mentioned before it may be well worth to do some metal detecting in order to recover the fired cases which will provide some more info as for the nationality of the aircraft (US or GB) and maybe even telling more about the engagement distance though this will have to include some allowances.

Maybe some of your other members here can provide more insight or correct what I said here.


#18

And my apologies for not catching your response sooner.

The biggest problem with the San Khayom Bridge is so little information is available. This shows up in working with your question guide:

  1. Target: railroad rolling stock (assumed: there are no records available from the railroad).
  2. Moving or still: moving (assumed).
  3. Hour of day / position of sun: unk, as is the event date; no witnesses on the ground survive.
  4. Weather: unk.
  5. Presence of enemy aircraft: unlikely (the only confrontation between Allied and Axis aircraft over northwest Thailand was in Nov 1944, and all five Axis aircraft were downed, with only one Allied lost; the skies were controlled by the Allies except for some anti-aircraft batteries (or equivalent) areas around Chiang Mai and Lampang airports, and around two railroad bridges farther south. One B-25 on a bombing run over one of the bridges, that at Kaeng Luang, was shot down by an anti-tank gun, also in Nov 1944. Those sites were well known to aviators for their defenses (and sometimes notably ineffective: see Attack on Lampang.
  6. Site of attack: railroad passing through open rice fields (assumed: that’s what it is today).
  7. Was plane fired on: apparently so, by a 57mm round which hit the bridge superstructure (Point G), which suggests that the gun was out-of-range.
  8. Plane’s armament: only evidence is two shell holes, apparently from 20mm rounds.
  9. Plane’s available armament: unk.

20mm rounds would narrow the probable Allied aircraft operating over northwest Thailand to two: the Beaufighter and the P-38.

The probable range of dates is established by the presence of these two types of aircraft over Thailand: April 1944-end of war. That covers particularly 211 Squadron flying Beaufighters out of India and 449 Squadron flying P-38s out of China; but that list of two cannot be said to be exclusive. The recordkeeping system, at least via the Internet, is not that precise. Further, the odd Beaufighter or the odd P-38 flying out of its assigned or assumed assigned area cannot be ruled out.

The train should be considered a “target of opportunity”. Structural steel bridges weren’t targeted for destruction with 20mm shells. No specific train could be marked for destruction. Intel wasn’t that fast. Communication wasn’t that good. Even without direct interference from hostile aircraft, trains couldn’t run on any schedule. Locomotives very quickly went through the low-heat content junk wood which was stacked at nearly every station for fuel. Even water towers were being targeted by Allied aircraft. So neither water nor fuel supplies were reliable.

Metal detectors: while they’re not illegal, in this current state of martial law in Thailand, local law enforcers can be expected to err on the side of caution. I’ll wait for a more relaxed military and political atmosphere before making any search attempt. Anyway, I am not optimistic about success since the poverty in the area during and after WWII made metal scavenging a cash generating activity; and the current relative prosperity has allowed the accumulation of quantities of steel refuse from railroad operations along (and beyond) the right-of-way.

To the present: I finally came across a description of a strafing process on the 13th Bomb Squadron website: Combat Tactics: Strafing (Area). The aircraft used was the Douglas A-26/B-26 Invader, apparently for combat in Korea:

“. . . from a low level approach to the target. . . . a desired 320 mph. . . . At approximately 3,000 yards from the target, the pilot pulls up to 300 ft. above the terrain, spots his target, . . . At approximately 1200 yards from the target, the pilot enters a gentle dive, lines up the target in the sight and commences his strafing run. Firing bursts should be short, starting at 1,000 yards, and breaking off at 400 yards. Gently fan the rudder . . . to effectively cover the target area. . . . Airspeed . . . is the best defense against enemy ground fire while on a low-level strafing run. . . .”

I’m incorporating that into the webpage dealing with Point A at Possible sources.

I think with the general lack of information, or more accurately with my lack of access to information, operating as I do here in Thailand, I can’t go much farther on the topic of Point A (and Point F). My effort is necessarily limited to producing (at least) one plausible scenario to explain Holes A and F which I hope I have now done.

I would be interested in comments about the page as it now stands: San Khayom Bridge. I’ve still to update subsequent pages.


#19

Islandee, your work looks well researched, sourced and reasonably explaind and concluded on. Under the given conditions and with the eminent limitations by the many unknown factors and lack of availability of the actual combat reports hardly anything better can be produced.

Maybe you can contact US and UK archives for further research?

Are you cooperating with a govt. museum in Thailand maybe? If so they may grant you an explicit permit for doing some detecting around the bridge?

Did Japanese trains have installed AA guns?

Maybe you can get photos of 20x110 HS cartridge (AP, “ball” and HE types) to show them with the penetrated bridge parts or the diagrams of the cartridges?


#20

EOD: I thank you. First I’ll finish cleaning up / updating my subject webpages with existing information that I have in hand. Then I’ll proceed further, using your suggestions, and check back in as work continues.


#21

Last but not least I wonder if you could cite the IAA (iaaforum.org) maybe? Or did I just miss it?


#22

IAA is covered, no problem, my pleasure. So far, see my page 1a, notes A07, A07a; and page 1b, note D05Ƌ. IAA is also cited on page 2b in notes L27 and L30, but I haven’t uploaded that page yet.


#23

I’m in the process of writing up what all I have to date on the two 20mm shell holes in the San Khayom bridge. I still have to deal with the 57mm shell hole (Point G).

I’ve not found as yet any aircraft, either Allied or IJAAF, operating over Thailand that used a 57mm cannon. On the ground, the Japanese had a Type 97 57mm Tank Gun, used in a Type 97 Medium Tank “Chi-Ha”. The gun would have been firing at the RAF Beaufighter or USAAF P-38 which was putting the 20mm holes in Points A and F of the bridge. The scenario in itself is not farfetched: 170 km SE at the Kaeng Luang Bridge, an enterprising Thai gunner using an anti-tank gun shot down a B-25. But at the San Khayom bridge, no Allied plane was downed though it might have been targeted.

I’ve found no record of tanks with 57mm guns or independently-mounted (jury-rigged) 57mm tank guns having been assigned or used at Lamphun; however, I see two possibilities by which such a tank or tank gun might have been present to defend the Lamphun bridge (plus a longer bridge just 6 km north):

  1. One of the main IJA supply routes for Burma followed the railroad from Bangkok to Lampang, 80 km south of San Khayom, where goods were transferred to road vehicles for transport to Kengtung, on to Mandalay, and then in 1944 to Imphal/Kohima, etc. There is also a story that an alternate supply route continued north by rail to Chiang Mai where goods were transferred for transport north into Burma. In both cases, rail transport came under heavy attack by Allied aircraft starting in early 1944 (there doesn’t seem to have been much recorded of attacks on road convoys). I’m guessing that those Allied air attacks might have damaged one or more tanks or their carriers sufficiently that they were abandoned along the way. Afterwards, enterprising Thais or Japanese might have salvaged a tank, or a tank gun, for anti-aircraft defense at Lamphun.
  2. In preparation for defending Thailand very near the end of the war, various IJA units were assigned to the general Chiang Mai area to meet any Allied ground attack from the north. IJA units included elements of the 4th and the 56th Divisions as part of the 15th Army which was itself headquartered in Lampang. All were essentially in position by June 1945. These units might somehow have acquired some Type 97 Medium Tanks, or at the least a Type 97 57mm Tank Gun, which found its way to the Lamphun area.

While this is totally speculative, I do have the hole in the bridge which records the diameter of the projectile, its angle of impact, and its bearing. If I could get a set of ballistics curves for the tank gun, I might be able to estimate the location of the gun, if it had been fired from the ground, and check that ground for any possible evidence (that’s where the metal detector will be a necessity).

So I ask, [color=#FF0000]does anyone have or know how to get ballistics curves for this Type 97, 57mm tank gun?[/color]

I thank you.


#24

Great, I just thought it could be a good idea to have the IAA cited in a well researched article.


#25

[quote=“islandee”]I’m in the process of writing up what all I have to date on the two 20mm shell holes in the San Khayom bridge. I still have to deal with the 57mm shell hole (Point G).

I’ve not found as yet any aircraft, either Allied or IJAAF, operating over Thailand that used a 57mm cannon. On the ground, the Japanese had a Type 97 57mm Tank Gun, used in a Type 97 Medium Tank “Chi-Ha”. The gun would have been firing at the RAF Beaufighter or USAAF P-38 which was putting the 20mm holes in Points A and F of the bridge. The scenario in itself is not farfetched: 170 km SE at the Kaeng Luang Bridge, an enterprising Thai gunner using an anti-tank gun shot down a B-25. But at the San Khayom bridge, no Allied plane was downed though it might have been targeted.

I’ve found no record of tanks with 57mm guns or independently-mounted (jury-rigged) 57mm tank guns having been assigned or used at Lamphun; however, I see two possibilities by which such a tank or tank gun might have been present to defend the Lamphun bridge (plus a longer bridge just 6 km north):

  1. One of the main IJA supply routes for Burma followed the railroad from Bangkok to Lampang, 80 km south of San Khayom, where goods were transferred to road vehicles for transport to Kengtung, on to Mandalay, and then in 1944 to Imphal/Kohima, etc. There is also a story that an alternate supply route continued north by rail to Chiang Mai where goods were transferred for transport north into Burma. In both cases, rail transport came under heavy attack by Allied aircraft starting in early 1944 (there doesn’t seem to have been much recorded of attacks on road convoys). I’m guessing that those Allied air attacks might have damaged one or more tanks or their carriers sufficiently that they were abandoned along the way. Afterwards, enterprising Thais or Japanese might have salvaged a tank, or a tank gun, for anti-aircraft defense at Lamphun.
  2. In preparation for defending Thailand very near the end of the war, various IJA units were assigned to the general Chiang Mai area to meet any Allied ground attack from the north. IJA units included elements of the 4th and the 56th Divisions as part of the 15th Army which was itself headquartered in Lampang. All were essentially in position by June 1945. These units might somehow have acquired some Type 97 Medium Tanks, or at the least a Type 97 57mm Tank Gun, which found its way to the Lamphun area.

While this is totally speculative, I do have the hole in the bridge which records the diameter of the projectile, its angle of impact, and its bearing. If I could get a set of ballistics curves for the tank gun, I might be able to estimate the location of the gun, if it had been fired from the ground, and check that ground for any possible evidence (that’s where the metal detector will be a necessity).

So I ask, [color=#FF0000]does anyone have or know how to get ballistics curves for this Type 97, 57mm tank gun?[/color]

I thank you.[/quote]

Hitting an aircraft with an AT gun is almost a miracle and I wonder of there are any more documented incidents like this. So using abandoned tanks (their main guns) for air defense is something extreme unlikely as they would have no military value in this role. Desperate shots of course can not be excluded.

Regarding that large hole in the bridge it should be kept in mind that it may not be a from a 57mm projectile at all nor has it to be related to the actual strafing run which produced the 20mm holes.
It might be worth to investigate what IJA units were deployed in the vicinity of the bridge (like 6km radius) during the war. That also brings us back to combat reports where one could try to investigate any other combat action in this area.


#26

One thought! It is not clear to me that the P-38 20mm was fired separately from the .50Bs. I have seen the P-38 cockpit and do not remember noticing a selector switch to separately fire the two types of nose armament, but it is logical that there could have been one.

Regardless of whether a P-38 pilot had the ability to separately select the guns, I can’t imagine why a pilot would strafe a train, using only the 20mm. The .50Bs on B-25s were known to take large bits out of the side of Japanese destroyers according to accounts I have read, and were regularly used against trains in Europe with great success. The lack of .50 impact marks on the bridge would strongly imply that the attacking aircraft were Beaufighters. If there were .50 impacts they would strongly imply a P-38, or more than a single attack. The USAF Museum in Dayton Ohio could likely answer the question on a P-38 selector switch, though the existence of such a switch is not central to your research.

Just some random thoughts.

Cheers,
Lew


#27

If you haven’t already done so, a search of the UK National Archive records for 211 sqn may prove useful. While researching RAF 115 sqn, I was absolutely amazed at how much information was contained in the RAF combat reports and operation records books. I shouldn’t have been surprised but in a number of cases, statements made on various websites were either not supported by the official records or were simply wrong.

NATO Dave


#28

[quote=“Lew”]One thought! It is not clear to me that the P-38 20mm was fired separately from the .50Bs. I have seen the P-38 cockpit and do not remember noticing a selector switch to separately fire the two types of nose armament . . . .
[/quote]
Rather than a selector switch, there were two separate buttons on the front and back of the control wheel at about 2 o’clock. The cannon trigger button was on the pilot side of the wheel. The machine gun button was at the same 2 o’clock, but on the “forward side of the wheel”. See Pilot’s Flight Operating Instructions for Army Models P-38H Series, P-38J-5 and F-5B-1, Figure 4, Item 12, page 3.

The thought should appear applicable to both P-38s and Beaufighters? In any case, why the pilot didn’t go in with all guns blazing is an unknown. Or, if he did, why there isn’t evidence of same in the bridge, another unknown. Perhaps some of the markings on the bridge which are so obscure that I’ve arbitrarily classified them as fabrication errors (and disregarded them) are ‘dings’ from 50s, but that certainly wouldn’t fit the damage 50s did to Japanese destroyers, which probably had some armor plate while the San Khayom was made of (soft) structural steel.


#29

None documented at least in Thailand that I’m aware of. Which I suppose could be cited as verifying the extremely long odds involved which made the event “almost a miracle”.

Nor can desperate measures: I recall reading that Allied pilots witnessed Japanese troops, rather than running for cover during a strafing run, apparently ordered out into the target area to shoot at incoming enemy aircraft with anything available, from pistols to rifles to MGs, and whatever else could be brought to bear. The Japanese army, at least the officers giving such commands, had a different perspective on the value of the lives of their charges from that of Allied and German military personnel.

Very true: I must include that in my writeup.

Elements of the IJA’s 4th and 56th Divisions were called into the northwestern Thai provinces, commanded by the 15th Army relocated to Lampang, in the last days of the war to defend against an Allied invasion from the north (Burma’s Shan States). I must add that detail to my writeup. There is even an old Thai in the village who recalls four or five IJA troops having been bivouacked in the local temple; but other details, if he ever knew them, are lost. The official Japanese military history of the war (I have those volumes which deal with Burma and Thailand), can only deal in relative generalities regarding that activity. Practically speaking, the language barrier limits my digging further. And even if unit records exist, they probably won’t be in any greater detail than Allied records which are notably absent when it comes to details like who exactly strafed a train 7km southeast of Lamphun rail station, with detail about a bridge not relevant and probably not mentioned. With the disorganization of the IJA in those latter days of the war (and the Allies broadbrush command to its aircraft to attack ‘targets of opportunity’), I don’t think such details exist.