Conversation so far:
When did Philip join the military?
After leaving Gordonstoun in 1939, Philip joined the Royal Navy.
Did he serve in any war?
During the Second World War, he continued to serve in the British forces.
When did he retire from the forces?
In January 1946, Philip returned to the United Kingdom on the Whelp, and was posted as an instructor at HMS Royal Arthur, the Petty Officers' School in Corsham, Wiltshire.
Did Philip go to college?
graduating the next year from the Royal Naval College, Dartmouth, as the best cadet in his course.
Were there other wars that he was involved in?
After the invasion of Greece by Italy in October 1940, he was transferred from the Indian Ocean to the battleship HMS Valiant in the Mediterranean Fleet.
Was he in the force with other royals?
two of his brothers-in-law, Prince Christoph of Hesse and Berthold, Margrave of Baden, fought on the opposing German side.
Was Philip ever promoted while in the force?
Philip was appointed as a midshipman in January 1940.
are there any interesting aspects in the article?
On 1 February 1941, he was commissioned as a sub-lieutenant after a series of courses at Portsmouth.

Question: What was the highest grade that he got to while in the navy?
Self-contained rewrite: What was the highest grade that Prince Phillip got to while in the navy?