[3] After the war, he held a number of brief appointments, including a period as tutor at HM Signal School, before being appointed, despite his lowly rank, to HMS Iron Duke in the spring of 1922 as fleet signal officer of the Mediterranean Fleet,[3] under the command of Admiral Sir Osmond Brock C-in-C.[2] He gained the rank of lieutenant-commander in 1924[3] just prior to his marriage to Patricia Hanbury, the sister-in-law of Herbert Fitzherbert, the executive officer of the Iron Duke[2] and was made a commander in 1928.

[3] Cunninghame Graham had the unusual experience of attending all three staff colleges: Naval at Greenwich 1929–30; Army at Camberwell 1930–31; and Air Force at Andover 1934.

[3] Having resigned himself, as had happened to his father, to remain a commander for the rest of his naval service,[2] he was promoted to captain, at the last possible juncture under the batch system then in force, on 31 December 1935.

[3] In January 1936, George V died and Cunninghame Graham, awaiting his first command, acted as aide-de-camp to Prince Paul of Greece[2] during his visit to London for the state funeral.

[2] As the diplomatic party were without any ciphering staff, it fell to Cunninghame Graham to inform the foreign secretary that the UK had declared war on Japan.

[2][3] In August 1943, he was promoted to commodore (2nd class) in charge of the Royal Naval Barracks, Chatham,[3] in command of 20,000 officers, men and women with a daily turnover of 1,000.

[2] Also during this time, he was an aide-de-camp to the King[4] (his father had been a groom-in-waiting to Edward VII and an equerry to George V) and was appointed a CBE in the 1944 New Year's Honours List.

[2] After the war he continued to command the 10th Cruiser Squadron (later 2nd Cruiser Squadron with his flag in HMS Superb), during which time he took part in the victory celebrations in the Netherlands and had the honour of having Princess Juliana and Prince Bernhardt as dinner guests;[2] he was also dispatched to Sweden on an official goodwill visit, being granted a private audience with King Gustav V.[2] In 1947, he became admiral superintendent at HM Dockyard, Rosyth.,[1] receiving a CB, and was promoted to vice admiral a year later.