Complex sentence: She disappeared in the Bay of Biscay while commanded by Günther Eppen sometime around January 31 1943, and the precise cause of her loss remains unknown, though the Bay of Biscay was at the time regularly patrolled by long-range Allied aircraft looking for U-boats.
Split into simpler sentences: She disappeared in the Bay of Biscay while commanded by Günther Eppen sometime around 31 January 1943. The precise cause of her loss remains unknown, though the Bay of Biscay was at the time regularly patrolled by long-range Allied aircraft looking for U-boats.