Complex sentence: By 14 September 1553 Willoughby and one other ship had become separated from Chancellor and completely lost, and the decision was taken to winter in a bay on the coast at a place now known to be on the Kola Peninsula in the general area of Murmansk.
Split into simpler sentences: By 14 September 1553 Willoughby and one other ship had become separated from Chancellor. As autumn had begun and they were lost, they decided to winter in a bay on the coast at a place now known to be on the Kola Peninsula in the general area of Murmansk.