Complex sentence: Their experience in sniping and street fighting caused Vaagso to develop into a bitter house-by-house battle causing the commander, John Durnford-Slater, to call in the floating reserve and troops from Maaloy Island.
Split into simpler sentences: Their experience in sniping and street fighting caused Vaagso to develop into a bitter house-to-house battle. This caused the commander, John Durnford-Slater, to call in the floating reserve and troops from Maaloy Island.