Complex sentence: Initially both schools operated as separate institutions governed by a common Board of Visitors, in 1845 the Arsenal Academy in Columbia became an auxiliary to the Citadel Academy in Charleston; first year students attended the Arsenal then transferred to the Citadel Academy to complete their education.
Split into simpler sentences: Initially both schools operated as separate institutions governed by a common Board of Visitors, in 1845 the Arsenal Academy in Columbia became an auxiliary to the Citadel Academy in Charleston. First year students attended the Arsenal then transferred to the Citadel Academy to complete their education.