One of three sisterships: "Train Ferry No. 1" to "Train Ferry No. 3", built in 1917 for the British Army. Two of them were lost in WW II, "Train Ferry No. 2" was shelled and beached off St. Valéry-en-Caux 13.06.40, while "Train Ferry No. 3" (renamed "Daffodil" in 1940) was mined off Dieppe 17.03.45 and sunk the following day.
The first one built, "Train Ferry No. 1", was renamed "Iris" in 1940, "Princess Iris" in 1942, "Essex Ferry" in 1946 and "Essex Ferry II" in 1956. She went to the breakers in 1957.
As far as I know the first big French owned trainferry was the "Twickenham Ferry" of 1934.
A (bad) picture of "Train Ferry No. 2":
http://www.photoship.co.uk/JAlbum%20Shi ... No2-01.jpg
and a picture of "Train Ferry No. 1" somewhat rebuilt as "Essex Ferry II":
http://www.photoship.co.uk/JAlbum%20Shi ... 0II-01.jpg