Complex sentence: Afterwards he served in the Mediterranean under Captains John Byng, Vanbrugh, and Lord Augustus Fitzroy; and in March 1739, being then a midshipman of the Somerset, was made lieutenant in the St. Joseph prize by Admiral Haddock.
Split into simpler sentences: Afterwards he served in the Mediterranean under Captains John Byng, Vanbrugh, and Lord Augustus Fitzroy, as a midshipman. In March 1739, being then a midshipman of the Somerset, he was made lieutenant in the St. Joseph prize by Admiral Haddock.