'Rainbow' (ii) was the Chinese offensive by General Wei Li-huang’s 'Y' Force down the Salween river in southern China and northern Burma (10 May/August 1944).

Undertaken at the instigation of Lieutenant General Joseph W. Stilwell with the full approval of Generalissimo Chiang Kai-shek, 'Rainbow' (ii) was designed to put into Chinese hands the region containing Myitkyina, Bhamo and Lashio, so easing the overland supply route to China.

The offensive was entrusted to the 'Y' Force, which comprised General Huang Chieh’s 11^th Army Group and Lieutenant General Huo Kuei-chang’s 20^th Army Group with some 72,000 men in 12 divisions for the short-term objective of taking Tengchung, Lungling and Mangshih in order that the Chinese would have the stretch of the Burma Road lying to the west of the Salween river, thus making it possible to place in service the complete supply route as soon as Stilwell’s Northern Combat Area Command had taken the Burmese portion.

Planned by Wei, the offensive lacked any real co-ordination, for while the 20^th Army Group was to cross the Salween river and advance over the Mamien and Tatangtzu passes in the Kaoli Kung mountain range to reach the Shweli river for a drive on Tengchung, the 11^th Army Group was to move as three separate entities with the 39^th Division of the 2^nd Army crossing the Salween river to the north of Hueijan in order to take the Hungmushu pass in the southern Kaoli Kung range and attack the remains of the Hueijan bridge from the rear, the rest of the 2^nd Army crossing the Salween river to the south of Pingka for the capture of this town and then Mangshih, and the 71^st Army following the 2^nd Army before diverging for the capture of Lungling.

The Japanese defence was entrusted to Lieutenant General Yuzo Matsuyama’s 56^th Division of Lieutenant General Masaki Honda’s 33^rd Army, and this formation had a strength of only some 11,000 men to face a Chinese force which was numerically very superior but which was, however, very short of supplies and ammunition for a campaign of the protracted nature which seemed likely.

The 53^rd and 54^th Divisions of the 20^th Army Group got under way on 10 May, but were soon stalled in front of the Mamien and Tatangtzu passes, which the Japanese had covered with permanent fortifications. The 2^nd Army, with the 88^th Division of the 71^st Army under command, made good initial progress and invested Pingka on 17 May before sending its main strength to establish a block on the Burma Road to the south-west of Mangshih, so cutting the 56^th Division's lines of communication, and to invest Lungling. The 71^st Army now followed the 2^nd Army across the Salween river and joined the 88^th Division for an assault in Lungling; this effort was bloodily repulsed between 9 and 13 June, and the Japanese commander now switched his main defence farther to the south in order to re-secure his severed communications, leaving only small forces to hold the Mamien and Tatangtzu passes.

Matsuyama moved with considerable speed, and by 14 June was in a position to counterattack at Lungling, driving the 10,000 men of the two Chinese divisions back into the hills by 17 June. To compound the problems of the Chinese, the 2^nd Army at this juncture decided to abandon its block on the Burma Road (on the grounds that it had not received its fair share of available army supplies) and fell back to Pingka. The 56^th Division thus secured its lines of communication, though the 20^th Army Group at this time broke through the Mamien and Tatangtzu passes and headed for the Shweli river valley and its important centre of communications at Tengchung. The 39^th Division had also made progress to secure the eastern side of the Hungmushu pass, but instead of being advanced to attack Hueijan as planned, it was diverted to the south in order to attack Lameng.

By the end of June the Chinese were thus outside Tengchung, Lameng and Pingka, but were unable to press their offensive with any real vigour. Matsuyama now had single battalions invested in Tengchung, Lameng and Pingka, but had the rest of his force (minus 3,000 casualties) to the west of the stalled Chinese. All Wei Li-huang could do at this time was to press ahead with the sieges of Tengchung, Lameng and Pingka. By the third week in July the 20^th Army Group had five divisions outside Tengchung, and with the aid of bomber support from Major General Claire L. Chennault’s US 14^th AAF the army group fought its way into the walled town on 4 August. Even so, Japanese resistance continued for another month; the same type of battle was waged at Lameng, where the 11^th Army Group was still outside the walls during August.

'Rainbow' (ii) had thus failed to secure the swift advantage demanded of it in southern China, and the campaign in northern Burma was further delayed as a consequence. It was only when the Northern Combat Area Command began its own offensive on 15 October that the 'Y' Force was able to get under way once more.