Complex sentence: Superheating of the boiler was first applied to number 3702, Halifax in June 1910 whereas top feed was introduced in 1912 and new cast iron chimneys in 1921.
Split into simpler sentences: Superheating of the boiler was first applied to no.3702, "Halifax" in June 1910. Top feed was introduced in 1912 and new cast iron chimneys in 1921.