English Officers in Indian Outfits

My wife's grandfather, the late Colonel Sebastian Witherington served in WWII in the Jammau-Kashmir Rifles. At some point in the War, probably early, he was captured by the Germans. He spent most of the War as a POW in a German camp. Just after the War, he returned to Kashmir and died of an aggravated ulcer. The family (his son, my wife's father is now deceased as well). I am looking for any further info regarding him, specifically, and generally the JK Rifles. Please advise.