Genealogy / Tracing my Polish ancestors? My fathers Polish surname is Daj [13]

i am looking to trace my polish ancestors, my dad came here after the war in june 1946, he gave his previous address as Naples. Unfortunetley my father passed away in 1970 aged 48, i was only very young at the time. The only info i have are his discharge papers from the Polish Resettlement Corps, not a lot to go on i know. He lists his address as Karczew i am aware that he mentioned a sister and a step-brother, so there could be relatives. I am finding it difficult knowing were to start my search, my fathers polish surname, (Daj) seams to be very rare and i have not bin able to trace it. My father was reluctant to discuss the war years but i do remember him telling me that the Russian troops attacked his home murdered his grandparents and parents and that he was forced to join the cavalry and was sent to siberia, somehow he ended up in Italy and from there the UK were he was in a camp he met my mother and married in 1949. If anyone can point me in the right direction to trace his life prior to coming to the UK i would be grateful.