Sweet find. If you are indeed a fan of history I would look into preserving that letter asap. It has some very interesting history connected to it. Simply put, this letter was sent to dissuade Sikh soldiers from joining the Azad Hind Fauj, the Free India Army. And promised them safe return and their old post back if they did.

Now for some context. World War 2 was a difficult situation for India and Indians. To begin with the population was starting to have enough of Indian Soldiers fighting in foreign wars. In WW1 alone India lost over 70,000 troops. The highest of not only all the British colonies, but any colony or non-European nation that fought in that war. There was also a general "Awaking" occurring in many parts of India. The Socialists in Punjab were outlining the atrocities committed by the British, and the humiliation that Indians were subjugated to by a foreign power. This struggle culminated when the crown hung Bhagat Singh. Gandhi's peaceful protests were garnering cross Indian attention. Folks who were not as far extreme to join the ranks of the socialists, but were for freedom, now had a new avenue of political power they can use. As you can see the Indian conscious is rising.

Now here comes World War 2 and the British begin to recruit heavily. The Sikhs were always at the top of the recruitment list next to the Gurkhas and Muslim Jatts, due to an outdated oriental Martial Race system where the British Mandated the heaviest of recruitment fall from the so called "Martial Races" who were seen to be better fit for combat due to their race and culture. These soldiers would be given incentives to join such as higher pay, quicker promotions, and retirement gifts of land and livestock. Young Indian men were desperate for these jobs though, even with their disillusion of the Empire and Crown. Thy had no choice, India was starving.

Not many people know this but the British orchestrated a mass and systematic starvation of the Indian people during World War 2. The biggest one occurring in Bengal where even the most conservative estimates put he death toll at 1.5 million people. The British policy at the time was very clear, they wanted to feed their soldiers above all. When Winston Churchill was asked about this famine he remarked "The famine was their own fault, for breeding like rabbits." This is also one of the more conservative things he had said. It went as far as to block countries like the US and Australia from sending aid to India during this era of famine. The reason is unknown, but in Madhusree Mukerjee's Churchill's Secret War, she outlines that this famine cause the number of recruits to jump up and caused the biggest "volunteer" army in world war 2.

This is where the Azad Hind Fauj comes into play. The Axis powers, mainly Japan, had this policy it set out early on the course of the war. It wanted to promote and strengthen Asia and asians as a people. After Japan joined the Axis powers and started the Pacific Theater it's main goal was to start to occupy European Colonies in the Pacific and Asia. Here they would spread propaganda of wanting to strengthen the occupied countries and fight out European influence, they would make it appear as if Japan was to be this Big Asian Brother who would help the nation achieve freedom, under Japan of course. And it worked. The people were tierd of being subjugated by white men from far away, they rose up and helped the Japanese. All over the Pacific Japanese-Asian led resistance forces were popping up. Now India is a little different here. India had already a history of struggle and Independence movements. There were many freedom leaders already living in exile who had clout. The biggest player being Subash C. Bose. He happened to find his way to germany and actually meet with Hitler. There he had convinced the Nazis to let him and his fellow expat Indians ally with the Axis powers and help create an army. He was granted permission and traveled to Japan via U-Boat to represnt Azad(free) India in the Pacific theater. The Japanese gave him a few islands and parts of captured Brumese India, money, and weapons. Here he began to train his forces of folks who were exiled or left India to fight for freedom, interestingly enough it was one of the only players involved aside from Nazi Germany and the Soviets who allowed women to fill combat roles. But the numbers still weren't good and Bose's army needed more people.

Here's where the POW's come into play. Japan and Indian forces were heavily involved in the Pacific theater fighting for control of South East Asia. This is where most of the British-Indian troops were sent and where the most Indian POW's were taken. These POW's were given an opportunity by the Axis. They could either die in the POW Camps, or fight for their countries liberation. I assume from this letter they were also told the British would kill/imprison them if they escaped and made it back, but I have no other sources to confirm this. So it's easy to see why the captured POW's would choose to enlist in the Azad Hind Army.

The reason Sikhs were one of the bigger forces to jump ship was due to Punjab being a hotbed of resistance. Many Sikhs had family member who were freedom fighters, or remember the Massacre of Amritsar(where British troops killed Innocent Punjabis at a gathering in cold blood, right next to a holy shrine) pretty well. But this letter has some castist, racial undertones as well. Like I stated earlier the Sikhs were a Martial RAce. So they were more valuable to the British. Sikhs were the ones who held most the officer positions. And it's interesting to see that put into practice in this letter.

I hope I answered your question and I thank you for sharing this letter. I'd love it if you'd be able to scan it. I'll list some sources below if you'd like some additional reading.

The Testimonies of Indian Soldiers and the Two World Wars: Between Self and Sepoy by Gajendra Singh.

The Indian National Army and Japan by Joyce C. Lebra

Churchill's Secret War: The British Empire and the Ravaging of India During World War II by Madhusree Mukerjee (HIGHLY RECOMMEND)