Complex sentence: In May 1929, Keyes took up the position of Commander-in-Chief, Portsmouth, the most important Home Command the Navy has, but he was very disappointed not to be made First Sea Lord in 1930.
Split into simpler sentences: In May 1929, Keyes took up the position of Commander-in-Chief, Portsmouth, the most important Home Command the Navy has. But, he was very disappointed not to be made First Sea Lord in 1930.