Complex sentence: Some of the landing party carried lighted gun-matches and, according to Trevelyan, had forgotten the possibility of a powder-magazine, but whatever the cause of the explosion the Allies suffered between 100--200 casualties.
Split into simpler sentences: Some of the landing party carried lighted gun-matches and, according to Trevelyan, had forgotten the possibility of a powder-magazine. Whatever the cause of the explosion the Allies suffered between 100--200 casualties.