Northwest Thailand during World War II

N 18°32.300
E 99°03.000
Ban San Khayom Bridge (Th: สะพานบานสันกะยบม / Jp: バンサンカヨム橋)
Page 6 of 11

Railroad Sta


Text Notes

Supplemental Information: the 20mm holes

Weaponry and platforms related to the 20mm caliber[M01]

Allied Forces

Aircraft armed with 20mm cannon are in blue boldface:

US mfgr:

P-38 Lightning: Apr 44-Mar 45
     4 x 0.50 in (12.7mm) cal BMG
     1 x 0.79 in (20mm) cal Hispano autocannon
     4 x M10 3-tube 4.5 in (112mm) rocket launchers

P-40 Warhawk: Jan 42-Mar 45
     4-6 x .50 in (12.7mm) cal BMG

P-47 Thunderbolt* (no specific reference)
     8 x .50 in (12.7mm) cal BMG
   10 x 5 in (127mm) "unguided" rockets

P-51 Mustang: Nov 44-Mar 45
     6 x .50 in (12.7mm) cal BMG
     6 or 10 x T64 5.0 in (127 mm) HVAR rockets (some models)

B-24 Liberator: Dec 43-Nov 44
   10 x .50 in (12.7mm) cal BMG
      (some models also had .303 (7.7mm) BMG)

B-25 Mitchell: Mar 44
   12-18 x .50 in (12.7mm) cal BMG
     8 x 5 in (127mm) HVAR rockets

Brewster F2A Buffalo: Jan-Mar 42
     4 x .50 in (12.7mm) cal BMGs

British mfgr

Westland Lysander: Feb 42
     4 x .50 in (12.7mm) cal BMGs

Hawker Hurricane: Mar 42
     4 x 20mm (0.79 in) cal Hispano Mk II cannons

Bristol Beaufighter: Mar 44-May 45
     4 x 20mm (0.79 in) cal Hispano Mk III cannons

     2-6 x 7.7mm (.303 in) cal BMGs
     8 x RP-3 "60 lb" (27 kg) rockets

Bristol Blenheim: Feb-Mar 42
     4-5 x 7.7mm (.303 in) cal BMGs

de Havilland Mosquito: May 45-end of war
     4 x .303 in (7.7mm) cal BMGs
     4 x 20mm (0.79 in) cal Hispano Mk II cannons

Axis Forces

While they were in friendly territory in Thailand, Axis forces might themselves have damaged the bridge; for example, an Axis aircraft shooting at an Allied plane which was attacking a train passing over the bridge. This list of aircraft types, with guns is all from Wikipedia; no Axis aircraft carried 20mm caliber weapons:

Vought O2U Corsair, biplane
     3 x .30 (7.62mm) cal BMG (one facing forward;
     two on a mount at the rear cockpit)

Curtiss Hawk II, Model P-6, biplane, fighter.
     2 x .30 (7.62mm) cal MG

Curtiss Hawk III, Model 68B, biplane, multipurpose.
     1 x .30 (7.62mm) cal BMG and 1 x .50 (12.7mm)

Martin 139W bomber.
     3 x .30 (7.62mm) cal BMG (located nose, dorsal, & belly positions)

Ki-15: Mitsubishi, reconnaissance ("Babs").
     1 x .303 (7.7mm) cal MG

Ki-21: Mitsubishi, heavy bomber ("Sally"/"Gwen").
     4 x .303 (7.7mm) cal MG (located nose, beam, & tail positions
     + 1 x .50 cal (12.7mm) MG in dorsal turret)

Ki-27: Mitsubishi, fighter ("Nate").
     2 x .303 (7.7mm) cal MG, or 1 x .303 (7.7mm) cal
     + 1 x .50 (12.7mm) cal MG

Ki-30: Mitsubishi, light bomber ("Ann").
     2 x .303 (7.7mm) cal MG
     (located one (fixed) in wing + 1 rear cockpit)

Ki-46: Mitsubishi, reconnaissance ("Dinah").
     1 x .303 (7.7mm) cal MG

Ki-55: Tachikawa, advanced trainer ("Ida").
     1 x .303 (7.7mm) cal MG (forward mounted)

It has also been suggested that non-aircraft mounted Axis guns might have made the 20mm holes. Prime candidates:

Anti-tank rifle: Type 97 Automatic Cannon 20mm (0.79 in) cal
AA/anti-tank gun: Type 96 AT/AA Gun 25mm (1 in) cal

Neither is likely to have been used in the area in question. There is no mention of anti-tank defenses in the area. Anti-aircraft responsibilities for railway structures early in the war were assigned to the Royal Thai Army's 35th Infantry Battalion, one company of which was equipped with heavy machine guns; and its definition of "heavy" apparently included 7.7mm as well as 12.7mm calibers.

To broaden the scope of the discussion about ground fire, the following:

In the Royal Thai Army (RTA) AA arsenal were 7.7mm, 12.7mm, 40mm, and 75mm calibers; which of those might have been around Lamphun is undetermined, though probably only the smaller calibers found their way north. Further, Lamphun airstrip was never a significant operation and was unlikely to have had assigned anything larger than 12.7mm guns.[M01a]

IJA AA weaponry included 7.7mm, 13.2mm, 20mm, 25mm, 40mm, 75mm, and 105mm calibers; but it is unlikely that IJA guns were ever present around Lamphun: the only possible attraction there for the IJA would have been the airstrip. However, the airstrip early-on catered only to the Royal Thai Air Force; and, while improvements there began in Nov 1943 --- which Allied intel attributed to the Japanese, the improvements were never completed.

Late in the war, Allied intel noted:


Partial transcription:

. . . A new development was encountered at Uttaradit and Lampang in the shape of flak-wagons, apparently attached to military trains. No flak-wagons had previously been identified in the SEA theatre except on the Burma-Siam line in April 1944.

The flak-wagons were never again mentioned in Allied intel reports. What weaponry they hosted (if any) is unknown.

Military Units

Allied Forces[M02]

Considerable difficulty was encountered in assembling this list, and it is, without doubt, incomplete:

A large number of units and aircraft were potentially involved. These units were very mobile, being constantly shifted around to best pursue an enemy shrinking in influence.

Many unit histories are summaries, and lack the detail to determine if particular subunits flew over Thailand.

Unit histories that do offer some detail often confuse Burma and Thailand: for example, the Thai bridges at Ban Dara and Kaeng Luang are often listed as if in Burma: this may be partly a result of the US trying to downplay Thailand's ambiguous position during the war --- and which the US notably brushed aside after the war. In any case, unit histories that mention Burma and not Thailand are at best meaningless and at worst misleading.

The intent was to identify unit designations from aircraft types; this was largely a failure since USAAF Chronos named aircraft types rather than units; however the effort did "find" British-operated Buffaloes, Mosquitoes, and Lysanders in other publications though not mentioned in the Chronos. There was also a vague possibility that air action at / around the bridge might actually have been recorded in after-action reports; but such has not been found (the effort is / will be akin to finding a needle in a haystack[M02α]). As best I can piece together regarding units operating over Thailand:

Nationalist Chinese Air Force

American Volunteer Group (AVG; aka "Flying Tigers") (1941-1942) (P‑40)

Tenth Air Force

2nd Air Commando Group (1944-1945)
2nd Fighter Squadron (many, most notably P-51)
7th Bombardment Group
436th Bombardment Squadron
492nd Bombardment Squadron
8th Photographic Reconnaissance Group
80th Fighter Group (P-38, P-40, P-51)
88th Fighter Squadron
89th Fighter Squadron
90th Fighter Squadron
459th Fighter Squadron

Fourteenth Air Force

312th Fighter Wing
33rd Fighter Group (P-38, P-47)
81st Fighter Group (P-40, P-47)
311th Fighter Group (A-36, P-51)
427th Night Fighter Squadron (P-61)
449th Fighter Squadron (P-38)[M02a]

IAF 1 Squadron (Lysander)
RAF 27 (F) Squadron (Beaufighter Vf)
RAF 45 Squadron (Blenheim)
RAF 67 Squadron (Brewster Buffalo)
RAF 89 (F) Squadron (Beaufighter VIf)
RAF 176 (F) Squadron (Beaufighter VIf)
RAF 177 Squadron (Beaufighter)
RAF 211 Squadron[M03] (Beaufighter X through May 1945)
                         (Mosquito, May 1945 and thereafter)

The AVG (American Volunteer Group, better known as the Flying Tigers), under the command of Claire Chennault at the beginning of the war flew several missions over Thailand. It is curious that the unit was absorbed into the 23th Fighter Group, also under Chennault's command, and frequently flew missions over Burma, but never again flew missions targeting Thailand.

Axis Forces

Military units in northwest Thailand included:[M04]

The Thais (FB (Foong Bin)= squadron):

FB 11: Ki-30
FB 12: Ki-30
FB 16: Hawk 75N & Ki-27
FB 21: Corsair
FB 22: Corsair
FB 32: Corsair
FB 33: Corsair
FB 41: Hawk II
FB 41: Hawk III
FB 42: Hawk III
FB 43: Hawk III
FB 52: Corsair
FB 61: Martin
FB 62: Ki-21
Support Wing: Ki-55

The Japanese:

12th Sentai: Ki-21
31st Sentai: Ki-30
77th Sentai: Ki-27
51st Independent Chutai: Ki-46
70th Independent Chutai: Ki-15

However, as noted above, no RTA or IJA aircraft had a 20mm gun.


Continued on next page







M01.^ Almost all information in this section came from the "Specifications" paragraphs of Wikipedia articles about the aircraft named.
















































M01a.^ What large calibers there were in the Thai military, were located around Bangkok and Sattahip --- not in northwest Thailand (Wisarut Bholsithi email of 1022 21 Mar 2014).

M02.^ The list developed from the following references is not complete. See Note [M02a] below for comment.

Maurer, Maurer, ed, Combat Squadrons of the Air Force: World War II (Montgomery AL: Maxwell Air Force Base, 1969).

Carter, KC, and R Mueller, US Army Air Forces in World War II: Combat Chronology 1941-1945 (Washington DC: Center for Air Force History, 1991).

CBI Order of Battle: 10th AF Bomber / Fighter / Commando / Liaison Units.

CBI Order of Battle: 14th AF Units.

The Warbird's Forum (Dan Ford)

Shores, Christopher et al, Bloody Shambles, Vol I, The Drift to War to the Fall of Singapore (London: Grub Street, 2002)

Shores, Christopher, Bloody Shambles, Vol II, The Complete Account of the Air War in the Far East (London: Grub Street, 2002)

Shores, Christopher, Air War for Burma, Vol III, The Allied Air Forces Fight Back in South East Asia (London: Grub Street, 2005)

Warbirds of India.

IAF No 1 Squadron.

Wikipedia: No 27 Squadron RAF.

Air of Authority - A History of RAF Organization: No 26 - 30 Squadron Histories.

Royal Air Force: 27 Squadron.

Wikipedia: No 45 Squadron RAF.

Air of Authority - A History of RAF Organization: No 41-45 Squadron Histories.

Wikipedia: No 67 Squadron RAF.

Air of Authority - A History of RAF Organizations: No 66-70 Squadron Histories.

Royal Air Force: 67 Squadron RAF.

Wikipedia: No 89 Squadron RAF.

Air of Authority - A History of RAF Organizations: No 86-90 Squadron Histories.

Royal Air Force: 89 Squadron.

Royal Air Force: 176 Squadron.

History of War: No. 176 Squadron (RAF): Second World War.

History of War: No. 177 Squadron (RAF): Second World War.

Royal Air Force: 177 Squadron.

Brown, AS, "Indian Days and Burmese Nights: Flying Beaufighters in Southeast Asia with 177 RAF Squadron" in Canadian Military History, 1995 (4:2:2), pp 14, 16, 22. Period: Mar-Dec 1944

Brown, AS, Silently into the Midst of Things (Victoria BC: Trafford, 2001), pp 104-105, 109, 183. Period: 14 Mar 1944-Feb 1945.

No 211 Squadron RAF.

Air of Authority-A History of RAF Organization: No 211-215 Squadron Histories.

M02α.^ With the guidance of NATODave post on International Ammunition Association forum topic "Terminal ballistics", I navigated the UK National Archives website to finally identify 66 file collections which might contain information regarding San Khayom. That represents an investment of £200+, rather dear to follow up a mere possibility (there is a limit to my largesse).

M02a.^ The USAAF 23rd Fighter Group's 449th Squadron does not appear in the references above, since none listed Thailand as a target for the 449th (if the unit was even listed). In actual fact, Thailand was one of its targets. This was brought to my attention by Daniel Jackson, author of the aptly named The Forgotten Squadron (Atglen PA: Shiffer, 2010), pp 51, 93-95, 97, 144, 150. [Dan Jackson email correspondence starting 1549 hrs 01 Jul 2014] This strongly suggests that there are other omissions.

M03.^ Beaufighters squadrons were first suggested by Jim Broshot, 2001 hrs 23 Mar 2014 post on Tullys Port at CombinedFleet.

M04.^ Young, EM, Aerial Nationalism (Washington: Smithsonian, 1995), pp 173-219.