Complex sentence: In 1941, whilst working as a secretary in Barry, southern Wales, Doreen married Joanis Vlachopoulos a seaman in the British Navy; during World War II he was declared missing and presumed dead.
Split into simpler sentences: In 1941, whilst working as a secretary in Barry, southern Wales, Doreen married a seaman called Joanis Vlachopoulos. He was a part of the Navy and during World War II was declared missing and presumed dead.