Complex sentence: The snort mast on the "Affray" was designed for both air intake and exhaust vent, this was later changed so the snort mast was an air intake only and the exhaust was moved to the rear of the conning tower.
Split into simpler sentences: The snort mast on the "Affray" was designed for both air intake and exhaust vent. At this was later changed so the snort mast was an air intake only and the exhaust was moved to the rear of the conning tower.