Complex sentence: At Sachsenhausen, he found himself with 3 other survivors of the'Great Escape' (Harry Day, Johnnie Dodge and Bertram James) and was placed in Sonderlager A (Special Camp A) within the main camp.
Split into simpler sentences: At Sachsenhausen, Dowse found himself with three fellow survivors of the'Great Escape': (Harry Day, Johnnie Dodge and Bertram James). They were placed in Sonderlager A (Special Camp A) within the main camp.