Complex sentence: The "Dolfijn" class submarines of the Royal Netherlands Navy are a class of four submarines, the "Dolfijn", "Zeehond", "Potvis" and "Tonijn", Which were built in the late 1950s and the early 1960s.
Split into simpler sentences: The "Dolfijn"-class submarines of the Royal Netherlands Navy are a class of four submarines; "Dolfijn", "Zeehond", "Potvis" and "Tonijn". They were built in the late 1950s and the early 1960s.