When it comes to sheer hardship under appalling combat conditions, it is hard to match what the 5307th Composite Unit (provisional), better known as Merrill's Marauders, endured in the China-India-Burma campaign.
When the Japanese had overrun and taken Burma from its colonial master Great Britain in 1942, it had cut the only real overland route for military supplies heading to Chinese forces fighting the Japanese in mainland China. The famed Allied air transport route "over the hump" of the Himalayas was no substitute for a reliable road considering the amount of supplies needed.
U.S. President Franklin Roosevelt and U.K. Prime Minister Winston Churchill decided at a conference in August 1943 to form special American units for infiltrating Burma, modeled after the British Army Chindits, a long-range penetration unit that had already operated in Burma under Brigadier Ord Wingate. The plan was to disrupt Japanese communications and supply lines and capturing key points, the reopening of the Burma Road could be accelerated.
An Army-wide call for those interested in volunteering was put out under presidential authority, drawing about 3,000 recruits from stateside units. Many were specifically drawn from soldiers who already had experience in jungle fighting from earlier in the war. After assembly in India, they received months of intensive training in jungle warfare under the instruction of Wingate, including extended exercises with the Chindits. The 5307th was placed under the command of Brig. General Frank Merrill, the source of the name 'Merrill's Marauders' eventually given to the unit by the press.
Conceived as a mobile raiding force, the Marauders were lightly equipped by conventional infantry standards, with no heavy weapons beyond light mortars, bazookas, and machine guns. Dense jungle and mountains made ground vehicles impossible, so supplies were to be carried by the soldiers themselves and hundreds of mules and horses. Resupply was limited to airdrops and whatever the unit could forage off the countryside in trade with indigenous locals.
Embarking on Feb. 24, 1944, the Marauders mission began with 2,750 men marching over a thousand miles through the Patkai region of the Himalayas, in order to get behind Japanese lines in Burma. Operating with indigenous Kachin scouts and Chinese forces, they began a series of raids against Japanese patrols, supply lines, and garrisons. Their ultimate goal was to capture the strategic Burmese town of Myitkynia, which had an important airfield and was along the route for an alternate road to China.
The Marauders were almost always outnumbered and outgunned by the Japanese 18th Division, which formed their primary opposition. Lacking artillery and out of range of any serious air support, they had to rely on surprise, training, and mobility to outfight the Japanese regulars, and they often found themselves on the defense because they were ill-equipped for fighting against larger forces.
But their greatest enemy, which inflicted more damage than even superior Japanese forces could, was the jungle. Malaria, amoebic dysentery, and typhus took an awful toll, inflicting more casualties than Japanese fire did. Soldiers shaking from fever and tormented by diarrhea had to force themselves through dense jungle and intense close quarters combat. Torrential rains, stinging insects, and snakes only added to their misery.
The issued K-rations were relatively light and compact, but at 2,900 calories per day were wholly inadequate for heavily loaded men marching, sweating, and fighting in the jungle. Even for men facing hunger, many components of the rations were so widely detested that they were often thrown away, and failed air drops only made the situation worse. Malnourishment and its accompanying weakness and exhaustion made the troops more vulnerable to already endemic diseases, and many of them were reduced to little more than walking skeletons.
Despite the enormous challenges, the Marauders managed to inflict far greater casualties on the Japanese then they suffered, and used their mobility and seeming ability to strike anywhere to throw Japanese forces into confusion. After dozens of skirmishes and several major actions, the 5307th managed to take the airfield at Myitkynia in August 1944 alongside elements of the Chinese Army, and the town itself after reinforcements arrived.
So decimated were the Marauders by disease and combat that only 200 men of the original task force were still present at the end of the campaign. Frank Merrill, who suffered a heart attack before being stricken with malaria by the end of the mission. Every last member was evacuated to hospitals to recuperate from months of hunger, disease, and exhaustion.
The 5307th was disbanded shortly thereafter, and in a very rare distinction every single member of the commando force received the Bronze Star for staying and fighting. They fought five major actions and dozens of smaller ones while marching over 750 miles through enemy territory, all the while fighting a different but even more deadly battle against hunger and disease. The unit was eventually redesignated as the 75th Infantry Regiment, from which today's 75th Ranger Regiment descended.