The Maryland was the forerunner of the Baltimore.
No.13 Squadron was not a unit of Coastal Command whilst operating in the Mediterranean Theatre. Gibraltar was the last Coastal Command station in that direction.
Whilst in Italy No.13 was part of No.3 Wing, South African Air Force, which in turn was part of the Desert Air Force.
This evening I have looked online for photographs of Desert Air Force and Mediterranean Allied Air Force Baltimores and that in few examples I found every one was marked with a single individual identity letter and wore no squadron code letters.
I concede therefore that my suggestion that the single letter may indicate a Communication unit was entirely unhelpful.
Tony Broadhurst