Complex sentence: The first British ship to reach the Java Sea was the 32-gun frigate under Captain Edward Elphinstone, which--in company with the brig-sloop under Commander Edward Troubridge--arrived in July 1806, cruising in search of Dutch activity in the area.
Split into simpler sentences: The first British ship to reach the Java Sea was the 32-gun frigate under Captain Edward Elphinstone, which arrived in July 1806. In company with the brig-sloop under Commander Edward Troubridge, the two vessels cruised in search of Dutch activity in the area.