Pai Bridge

The Pai River bridge is often cited as the most visible evidence of the presence of Japan's Army in Northern Thailand during WWII.
But the bridge was actually built after the war. This website attempts to correct both that misconception and others about the period.


Japan in Northwest Thailand during World War II

Mae Mo[1a] Landing Ground (Th: ท่าอากาศยานแม่เมาะ / Jp: マイモ滑走路)
Lampang Province
Page 1 of 4
Thai Route 0001
Sta 000.00 [2]
offset 0.8km south


Text Notes


Mae Mo: Summary

Mae Mo Landing Ground was the easterly satellite air facility in the Lampang Airfield Group of the Imperial Japanese Army Air Force (IJAAF). The facility's two runways, the better developed one running NNE-SSW, and the other N-S, formed an "X". It was located approximately 31 km by air northeast of Lampang Railway Station (the reference point used by Allied intelligence during WW2), and about 28 km by air from the Lampang runway. Constructed by the Japanese in 1944-1945, no aircraft was ever observed there. There is evidence on the ground and in local oral history of at least one effective Allied targeting of the facility. After the war, surrounding forests which best defined the runways were cut down, with the runways themselves almost disappearing into the rice field panorama that now covers the immediate area.

General location map for Mae Mo

Aerial photo flight reports below record coverage of Mae Mo Airstrips (Memoh Landing Ground) by only the 21st Photographic Reconnaissance Squadron (21PRS). Other coverage probably exists, but records seem not to have been released as yet. No WW2 era photos of the facility have been found either (other than the extremely poor quality mimeographed (?) copy published on 11 November 1944 and shown below, and republished in January 1945 as seen on the next page).

February 1944

21PRS, based in Kunming, China, was one Allied unit that made aerial photographs of features in Thailand. The Mae Mo airstrip was about 800 km (500 mi) SSW of Kunming. One of the areas targeted in this aerial photo request below was not named, but the only site anywhere close to the specified 13 miles (21 km) northeast of Lampang was Mae Mo, which was actually about 19 miles (31 km) away (as measured to the Lampang railway station):


07 March 1944: The diagram below stands out as unusually crude amongst most other Allied intel graphics (for example, compare another map of the same area in Feb 1945). The manner of presentation suggests an unscaled schematic rather than a map. It places the Mae Mo airstrip close to the railway station, while it was actually 16 km (10 mi) south. The bearing of the railway track at Mae Mo Station is 45°-225°, not east-west as shown in the sketch. It seems probable that the crudity of the sketch was the result of a source "on the ground" who was not familiar with the rigors of map making. Note that the publisher was the South-East Translation and Interrogation Center:

Earliest diagram of Mae Mo[4]

April 1944

In a comprehensive table published in January of the next year about the Lampang Airfield Group --- of which Mae Mo was a part --- the Mae Mo air facility was recorded as having been first observed on 25 April 1944. Curiously the April date was about two months after the two reports above were dated. No explanation has been found for the later use of the April date.

19 June 1944[4a]

341st BG unit records describe a task assigned to the 22nd Bombardment Squadron as Mission B­247, that of bombing the Kaeng Luang Railway Tunnel (assumed to have been the Huai Mae Lan tunnel):[4b]

19 Jun 44 – Four 22nd B-25s took off from Yangkai at 0700 hours to attack the Kenghluang Railway Tunnel, Thailand --- All planes succeeded in reaching the Kenghluang Railway Tunnel, which was observed through breaks in the clouds. These breaks, however, were neither sufficiently large nor frequent enough to permit a bomb run. . . .

Planes 43-3617 and 43-3958, after repeated attempts, finally located a break (in the clouds) and spotted an airfield having two runways crossing in an 'X' pattern. These two planes dropped all bombs on the airfield but results were completely obscured by the cloud overcast. . . .

In the north of Thailand, there was only one "X" pattern airfield: Mae Mo, and the current rice paddy terrain at the former site still displays bomb craters. Ironically Allied reconnaissance never observed any aircraft there. Note that the "X" pattern had not been designated for bombing, but had become a target only by accident. Lampang's other two satellite airfields, Hang Chat and Ko Kha were never attacked.

September 1944

Here, Allied Intel labeled Mae Mo as one of the three "most interesting" newly discovered sites "during the month" in Southeast Asia, and it was accurately located 19 miles ENE of Lampang (railway station) --- while billed as "newly discovered" this month (presumably September), recall that the sketch just above was dated six months earlier:


Within the same report, the location of Mae Mo airstrip(s) became a bit more fluid. The north (N) position coordinate is okay; the east (E) position coordinate differs with standards today, but that difference probably partly reflects the Indian datum used as a reference in Thailand at that time. The reference to Mae Mo Village is now obscure: if it was in fact located three and a half miles south of the airstrip(s), the village was subsequently totally enveloped by the open pit coal mine. The community currently bearing the name, Mae Mo, is about 16 km (10 mi) south) of the airstrip:


22 September 1944

Four days later there was a photo order that included two bridges south and southeast of Pakhem.[6a] The coordinates for Pakhem are provided in the order and place it 12 km (8 mi) southeast of the Mae Mo air facility. No photo information for the targeted bridges is described in the results. The results do describe "double L/S" (landing strips) nearby Pakhem and there is only one air facility in the area with such a configuration: Mae Mo.


21 October 1944: Construction was noted as continuing per an observation probably made 21 October 1944 (the same day as the comment preceding it which noted no aircraft having been observed during the period). The continuous reporting of construction observed in the previous six months implied a concerted effort to prepare the airstrips. The (J) following the title Memoh Landing Ground is the first indication that Allied Intelligence had evaluated the airstrip as being a Japanese effort, not a Thai one:


25 October 1944: Allied planners anticipating the Japanese army, on retreating from its failed invasion of India, would "hold its ground" in Burma with support from Japanese resources in Thailand, introduced the concept of the "Thailand Line of Airfields":

Thai line of airfields

Text of above (smoothed):


As in Burma considerable post-monsoon reclamation work is proceeding. Development of the Thailand Line of Airfields, an illustration of which is given overleaf [see below], continues and it is now clear that full preparations are being made for basing and operating aircraft from this sector as and when Allied pressure increases in Burma. This strategic line is capable of providing complete air cover to Rangoon and the Irrawaddy Valley.

The immediate zone for providing air cover to Northern Burma is the Shan Plateau area. The secondary zone will be the Chiang Mai Group at the Northern end of the Thai line.

North Thai ring of airfields

Text circled above (smoothed):

Mae Mo Landing Ground

• Airstrips of rolled earth are under construction.
• North-south. About 1700-1800 yards.
• Northeast-southwest. About 1700-1800 yards.
• Category C [liable to become unserviceable after rains]
• 0 aircraft shelters
• A new site in an early stage of construction

On 25 October 1944, an attempt to photograph Memoh A/F was unsuccessful due to cloud cover:


01 November 1944: Another photo request, just a week later, for Memoh failed due to cloud cover:


02 November 1944: In a third attempt in just over a week, targets in northwest Thailand, including the Mae Mo airstrips, were finally successfully photographed:



11 November 1944: The first aerial photo of Mae Mo was published, but was of such poor quality as to be unusable, at least now. It has here been reoriented so that photo north points to the top of this webpage:



And an interpretation on the same date noted evidence of continued construction:


19 November 1944: This schedule carried information valid "up to" 19 November 1944; ie, as of that date. First time information included runway and accommodation data:


15 December 1944: Interpretation of aerial photos became more detailed as the north-south runway neared completion:


31 December 1944: And, as interpretation became more detailed (as shown just above), in the same month, formality and detail of published information became more sophisticated:





Coordinates --- 18°25'N; 99°45'E
Altitude (feet above mean sea level) --- 1300 (approx)
Map Reference --- Siam 1/1,000,000 NE47 and 1/4" NE-47J
Local Position and Landmarks --- 3-1/2 miles north of [Mae Mo] village and 11-1/2 miles NNE of [Mae Mo] railway station; just south of Lampang-Chiang Rai main road and west of [Mae Mo] River; 19-1/2 miles ENE of Lampang railway station.
Landing Area (dimensions in feet) --- Runway and strip intersecting in form of X.
     Runway: NE-SW 5100 x 300 (approx)
     Strip    : N-S     5100 x 165 (approx)
Obstructions ---
Surface --- Runway being metaled; strip rolled earth.
Serviceability --- Runway will probably be all-weather, remainder serviceable in dry weather only. Heavy rains during SW monsoon, May to October.
Installations ---
     (a) Administration and Living Accommodations ---
            Temporary living accommodations in barracks to north
            of landing ground, and in village.
     (b) Hangars and Workshops ---
     (c) Storage ---
          (i) Fuel and Oil ---
          (ii) Bomb and Ammunition ---
          (iii) General Stores ---
     (d) Telephone, W/T, Signals, etc ---
     (e) Night Landing ---
     (f) Water ---
Aircraft Dispersal ---
     (a) Dispersal Areas ---
     (b) Aircraft Shelters: --- See "Record of Major Development"
Defenses --- See current report on "Japanese AA Defenses"
Access ---
     (a) Rail --- Nearest station [Mae Mo] (11-1/2 miles SSW) on
                      Chiengmai (Chiang Mai) - Bangkok line.
     (b) Road --- A first-class road just north leads WSW to
                        Lampang (19-1/2 miles) and NNW to Chiang Rai
                        (100 miles).
     (c) Water --- [Mae Mo] River
Additional Information --- Site still under construction.



Revision List
2013 Sep 15
First published on Internet
2014 Jan 05
Content materially expanded.
2015 Apr 20
Minor additions; bridge info separated out and put into new page 4.




These pages were composed to be best viewed with Google Chrome.

See Key for interpreting page content.

Revision list. See bottom of Text column on this page.

Bibliography supports notes.

1.^ Source: Combination of GPSs from site visit and Google Earth.

1a.^ During WWII: "Memoh". Uncommonly, "Memeh".

As an administrative district in Lampang Province, Mae Mo covers almost a thousand square kilometers. The name is best known as that of the Mae Mo open pit (opencast) lignite mine with the largest electrical generation facility in the north located next to it. A subdistrict and a railway station carry the same name and are near the power plant. This all proved very confusing in trying to locate the IJAAF Mae Mo airstrip, until Allied intelligence maps pinpointed its location, well north of that collection of names.

More correctly, it is in Ban Ta Sri, Tambon Ban Dong, Amphoe Mae Mo.

Note: not listed in Air America's Air Facilities Data Thailand 432, 1971.

2.^ By author inspection

3.^ "Terrain" map from Nations Online Project: Searchable Map and Satellite View of Thailand using Google Earth Data. Annotation by author using Microsoft Publisher.





3a.^ 21st Photographic Reconnaissance Squadron (hereafter 21PRS) Report Mission No. 14/23A, 26 Feb 1944 (USAF Archive microfilm reel A0878 p0118). There was more than one Allied unit charged with aerial photography over Thailand, but the only order sheets found to date are those from the 21PRS.

A short explanation of aerial photograph orders is at USAAF Aerial Photographic Intelligence.











4.^ Plans of Airfields in French Indo-China and Siam (Publication No. 3.II)
(South-East Asia Translation and Interrogation Center,
30 Nov 1944), Map No. 67, "Memoh Airfield 3 Mar 44" unnumbered page,
(USAF Archive microfilm reel A8023 p0453).





















4a.^ Detail for 19 Jun 1944 added 11 Apr 2015.


4b.^ Courtesy of Tony Strotman (mgr, website, 
341st Bombing Group
(Mission B-247. Operational Intelligence Report, CD A0543 image 916/page 938)














5.^ Airfield Report No. 26, Sep 1944,
"Comments on Current Airfield Development", p (ii)
(USAF Archive microfilm reel A8055 p0969).

























6.^ Airfield Report No. 26, Sep 1944,
"New Airfield Sites", p (v)
(USAF Archive microfilm reel A8055 p0976).


















6a.^ Pakhem no longer exists --- it was absorbed by the sprawling Mae Mo lignite surface mine whose product powers the Mae Mo Power Generation Plant. However, somewhat humorously, both mapquest (at N18°20.13 E99°43.90) and Satellite Views (at N18°20.15 E99°43.92) list the location. The coordinates compare reasonably well with the photo order's N18°20 E99°48. The latter source further describes Pakhem as a "City or Community: Populated place".

6b.^ 21PRS Report Mission No. 4 MA 118, 22 Sep 1944 (USAF Archive microfilm reel A0878 p0476).












7.^ Airfield Report No. 27, Oct 1944,
"Record of Airfield Activity and Development", p 9
(USAF Archive microfilm reel A8055 p1019).

Note that the last 21PRS photo mission over Mae Mo was dated 22 September 1944. The comment about "infrequent cover during the month" would appear to have spurred subsequent pointed efforts on 25 Oct, 01 Nov, and 02 Nov to photograph the site.















7α.^ Airfield Report No. 27, Oct 1944, "Comments on Current Airfield Development", "Thailand", p ii (USAF Archive microfilm reel A8055 p0998).

The term "Chiang Mai Group" in reference to WW2 airfields appears nowhere else in the literature. Its meaning is unclear.










7å.^ Airfield Report No. 27, Oct 1944, "Thailand Line of Airfields", unnumbered page (USAF Archive microfilm reel A8055 p0999).

















7a.^ 21PRS Report Mission No. 4 MA 132, 25 Oct 1944 (USAF Archive microfilm reel A0878 p0551).


8. (deleted).













9.^ 21PRS Report Mission No. 4 MA 136, 01 Nov 1944 (USAF Archive microfilm reel A0878 p0567).















9a.^ 21PRS Report Mission No. 4 MA 139, 02 Nov 1944
(USAF Archive microfilm reel A0878 p0568).

















10.^ Airfield Report No. 31, Feb 1945, "Memoh L/G" (dated 11 Nov 1944), unnumbered page
(USAF Archive microfilm reel A8056 p0014).



















11.^ Airfield Report No. 28, Nov 1944, "Record of Airfield Activity and Development", p 8 (USAF Archive microfilm reel A8056 p1133).



















11a.^ Airfield Report No. 28, Nov 1944, "Memoh Landing Ground", unnumbered page (USAF Archive microfilm reel A8055 p1081).



























12.^ Airfield Report No. 29, Dec 1944, "Record of Airfield Activity and Development", "Siam"
(data dated 15 Dec 1944),
p 7 (USAF Archive microfilm reel A8056 p1181).





















13.^ Siam (Thailand): List of Airfields and Seaplane Stations, "Memoh Landing Ground", (data dated to 31 Dec 1944) unnumbered page (Washington DC: Office of Assistant Chief of Air Staff, Intelligence, 1945)
(USAF Archive microfilm reel A1285 p1237).