Complex sentence: A huge problem during the transports were the prisoners cronical diarrhoea, after a while this was remedied by the Danes supplying portable closets of a type they had used during their transports.
Split into simpler sentences: A huge problem during the transports were the prisoners chronic diarrhea. After a while this situation was remedied by the Danes supplying portable toilets of a type that they had used during their transports.