Complex sentence: The planning of the JNR Class C63 began around about 1955; the choice of a steam locomotive was due to financial difficulties at JNR, making investment in electrification and diesel locomotives difficult.
Split into simpler sentences: The planning of the JNR Class C63 began around about 1955. The designers chose to develop a steam locomotive because of financial difficulties at JNR, which made investment in electrification and diesel locomotives difficult.