I saw the reference to your site in the Family Tree Magazine and thought I would write to you.
I had an uncle Cyril. I was named after him and he was named after Cyril Maud, the actor. He was a diesel engineer and back in the1930's (see - I am a bit older than you) I remember a Post Card of a steamship called 'Something Castle' on which he served. I was seven or eight at the time and the only other thing I remember about that PC was that the ship had two funnels. There isn't much I can tell you.
His full name was CYRIL KARL BLOUNT and his friends called him JACK. He was born 18th October 1907 in Crewe CHS. He used to sail out of Southampton where he met a nurse - Kathleen Frances Marshall and married her 8th April 1939. He was put on invasion barges during the war and was at Bone in North Africa when he was blown up and lost all his clothes. He was 'captured' by the Americans and put in an Italian PoW Camp. They thought his whiney North Staffordshire accent was Italian and he had a job proving he was British. After the war he worked on the docks at Southampton - I do not think he sailed. He died 21st March 1982 at Sholing, Southampton HAM.
But there is certainly a connection between him and a ship of the Castle Line during the 1930's.
On 7th of Feb Cyril wrote saying he thought the ship's name was "Warwick Castle" which I am sure is correct. The 'Warwick' as built had two funnels, she was sunk in 1942.