Military Prison Ship, Rouen

[Graham Mark]

Can anyone tell me a bit more about this ship please?
 
The card is addressed to Ulceby (spelled wrongly by the writer).
The pmk is APO 47 (Rouen) 8Jan15.  CM2/2000 not allocated by FWD.
The LtCol who signed the card in pencil was Percy Umfreville (1868-1922), Major Ryl W Kent, temp LtCol.  Governor 1st class 5Aug14-14Aug16.
Brev LtCol 3Jun17. Temp BrigGen 15Aug16.  Director of Military Prisons in the Field (graded AAG) 15Aug16.  Commdt 1st Class, Detention Barracks 22Aug17.
4 mentions, CMG 1915, CBE 1919.
Forgive me if you have seen this question before but I could not find an earlier entry by me on this subject on the forum.
Graham