Complex sentence: King's ships were built and equipped there to be used for trade as well as war, one of which accompanied him on his expedition to the Islands in 1429 and the office of Lord High Admiral was probably founded in this period.
Split into simpler sentences: King's ships were built and equipped there to be used for trade as well as war, one of which accompanied him on his expedition to the Islands in 1429. The office of Lord High Admiral was probably founded in this period.