Conversation so far:
When did Prince Philip, Duke of Edinburgh join the military?
After being educated in France, Germany and the United Kingdom, he joined the British Royal Navy in 1939, aged 18.
Did Prince Philip, Duke of Edinburgh serve in any war?
During the Second World War he served with distinction in the Mediterranean and Pacific Fleets.
When did Prince Philip, Duke of Edinburgh retire from the British forces?
His active naval career had ended in July 1951.
Did Prince Philip, Duke of Edinburgh go to college?
Philip completed a term as a cadet at the Royal Naval College, Dartmouth.
Were there other wars that Prince Philip, Duke of Edinburgh was involved in besides WWII?
After visiting London for the memorial, Philip and his mother returned to Greece where Prince Andrew had remained behind to command an army division embroiled in the Greco-Turkish War.
Was Prince Philip, Duke of Edinburgh in the British force with other royals besides himself?
Two of his brothers-in-law, Prince Christoph of Hesse and Berthold, Margrave of Baden, fought on the opposing German side.
Was Prince Philip, Duke of Edinburgh ever promoted while in the British forces?
On 16 July 1950, he was promoted to lieutenant commander and given command of the frigate HMS Magpie.
are there any interesting aspects in the Prince Philip, Duke of Edinburgh article?
Princess Elizabeth and the Duke of Edinburgh were both appointed to the Privy Council on 4 November 1951.

Question: What was the highest grade that he got to while in the navy?
Self-contained rewrite: What was the highest grade that Prince Philip, Duke of Edinburgh got to while in the navy?