Complex sentence: A total of 75 were built; 55 were built in four batches between 1906 and 1915 and a fifth batch of 20 locos was built in 1924, during Collett's tenure at Swindon.
Split into simpler sentences: A total of 75 were built; 55 were built in four batches between 1906 and 1915. A fifth batch of 20 locos was built in 1924, during Collett's tenure at Swindon.