I. B. 148
November 1, 1941.
Memorandum for the Chief of Staff:
Subject: Possible Japanese Drive into Yunnan. (For map see Tab A).
1. Recent developments in the international situation, and particularly in the Pacific, indicate the possibility of a Japanese invasion of Yunnan Province in an attempt to cut China's life-line, the Burma Road.
2. Factors which indicate possibility of such a line of action by Japan:
a The political and economic situation at home and pressure from the Axis demand action.
b. If she moved on Thailand, or elsewhere to the south, Japan runs grave risk of war with the ABD countries-an event which she wishes to avoid, at least for the present.
c. Japan's plan for conquest of Eastern Siberia would obviously best be served by a policy of watchful waiting until Russia is much weakened.
d. A drive from Indo-China into Yunnan would most probably not involve Japan with any third nation.
e. An offensive elsewhere in China could have no such decisive effect as the stoppage of supplies entering China over the Burma Road. This operation, if successful, might force capitulation of the Chinese.
3. Factors operating against such an offensive:
a. Japan is already extended in China where she has the equivalent of some 30 divisions spread so thinly that withdrawal of any troops for concentration elsewhere would seriously endanger her present lines. This was clearly shown in the recent operations at Changsha and Ichang.
b. Japan has perhaps 33 divisions in Manchuria and adjacent areas. To withdraw any considerable force from this region might cause her to "miss the bus" when her chance comes for invasion of Siberia.
c. Japan has the equivalent of some 3 1/2 divisions in Indo-China as garrison troops and to secure the Thai borders. Continuance of the bulk of these troops on this duty is necessary.
d. Similar considerations apply to the concentration of the Japanese air forces
e. Estimates of the initial force required for invasion of Yunan, from various sources, British, Chinese, Russian and American, vary from 5 to 10 divisions and all agree on the necessity of using strong air forces. Thus. a major effort would be necessary, including the use of many transports, supply ships, etc.
f. If Japan became involved in a long campaign in southwest China, she would be seriously hampered in operations elsewhere.
4. Physical difficulties in the way of a Yunnan invasion are considerable, the most important being the terrain. The best corridor is that followed by the Yunnan meter-gauge railway from the border at Laokai to Kunming. This is a tortuous route along the sides of deep gorges, from an elevation of 305 feet at Laokai to 4,500 at Mengtze on the Unnan plateau in a distance of 110 miles. (Airline, about 75 miles.) The dozens of bridges and tunnels have presumably been destroyed; the Chinese report that they have completely demolished the railway including the roadbed for a distance of 50 miles north of the border and partially for an additional 15 miles. There is a trail about 30 miles west of and roughly parallel to the railroad, but there is no road south of Mengtze. Only two other corridors exist, according to the Chinese Minister of War: one, an old road parallel to and about 30 miles west of the railway; the other about 120 miles east of the railway. The same source says that lateral travel between these routes is impossible because of the ruggedness of the terrain, and that the Chinese have rendered impassable all three routes of approach. Possible use of the valleys of the larger river appears remote.
The Red River flows from the Tali Lake, just north of the Burma Road 250 miles west of Kunming, southeastward into Indo-China at Laokai. It is not navigable north of Laokai. There is a trail running northward along the river to a point 60 miles above Laokai, where it branches northeast to Mengtze. A footpath extends on up the river all way to Tali. The terrain is extremely rugged. From the scanty information available, the valleys of the Black and Makong Rivers would be even less accessible.
5. Chinese preparations against an invasion of Yunnan from Indo-China include the demolitions mentioned above. For some time, two group armies have been stationed in southeastern Yunnan. These are:
1st Group Army: 6th Army Corps of 2 divisions; 60th Army Corps of 3 divisions.
9th Group Army: 52d Army Corps of 3 divisions; 54th Army Corps of 2 divisions.
Plus 2 independent divisions. These are regular troops, but the bulk are Yunnanese, who have not previously demonstrated superior fighting qualities. The commander of the troops in this area is General Kuan Ling-shenk who took part in the successful Changsha defense of 1939.
The Chinese lack artillery, are very short of ammunition, both artillery and small arms, and to all practical purposes are devoid of an air force.
The Chinese have lightly organized a position 20 to 40 miles in depth, with the main line of resistance along a generally east-west line about 50 miles north of Laokai. Their line of observation is along the border. Two other positions south of Kunming are being organized. The southernmost is about 30 miles south of Kunming.
6. It is estimated that at the present rate of Japanese reinforcement of their troops in Indo-China, a period of from one to three months will be required before they can have a sufficient concentration for an offensive against Yunnan.
7. The rate of Japanese advance on Kunming once the border is crossed, will depend on the degree of Chinese resistance, especially in their defense of the extremely rugged terrain between the Indo-China plain and the Yunnan plateau.
8. A Japanese offensive into Yunnan from Indo-China would be an extremely difficult operation but if it were successful in closing the supply route from Burma it would be a serious blow to China's power and will to resist .
Brigadier General U. S. Army
Acting Assistant Chief of Staff, G-2.
Tab A. 
Distribution: Chief of the Army Air Forces
The President Mr. Lauchlin Currie
Secretary of War Division of Defense Aid Reports
Secretary of State Director of Naval Intelligence
Under Secretary of War Assistant Chief of Staff, W. P. D.
Assistant Secretary of War G. H. Q.
Assistant Secretary of War Chief of the Air Corps
for Air Air Corps
Chief of Staff General Embick
Coordinator of Information
(EXHIBITS OF THE JOINT COMMITTEE, PHA, PT. 14, EXHIBIT NO. 33 MILITARY INTELLIGENCE ESTIMATES PREPARED BY G-2, WAR DEPARTMENT)