Complex sentence: The British and the French Fifth Army retreated August 23, and the town was besieged by German heavy artillery started August 25, and was surrendered September 7 by General Fournier, who was later court marshaled, but exonerated, for the surrender.
Split into simpler sentences: The British and the French Fifth Army retreated August 23, and the town was besieged by German heavy artillery starting August 25. The fortress was surrendered September 7 by General Fournier, who was later court marshaled, but exonerated, for the surrender.