Complex sentence: Sir Maurice Berkeley declined to take Pelham on at the Board of Admiralty in December 1856 due to his connections with Northumberland, but he did enter the Admiralty in November 1857 after Berkeley's retirement, though he then left it in March 1858.
Split into simpler sentences: Sir Maurice Berkeley declined to take Pelham on at the Board of Admiralty in December 1856 due to his connections with Northumberland. Pelham did enter the Admiralty in November 1857 after Berkeley's retirement, though he then left it in March 1858.