hi sandi15
it appears whoever told you about Japanese pow,s being marched across Europe is getting mixed up with allied pow,s being marched across Europe by there german captors with the Russians advancing pows in what became known as the death march in the middle of winter were forced to head west away from the Russians .do a google search for british pows force march you,ll find more info on several sites .
if you go to this site , veterans-uk.info/ from there you can download the necessary forms to apply for your granddads service record if he,s no longer with us then a death cert is needed and a fee of £30 if his wife is still alive she can get the record for nothing it does take a long time to process but all being well will give you more info on him .
also do a google search for british pows of the Japanese , numerous sites show up and I,m sure looking through them you will come to understand the reason why he refused to talk about it all and the inhuman suffering they endured .
yours
trevor