MBTA F40 Secondary Classifications

I was recently looking at an MBTA F40 and I noticed a small bit of text to the right of the ladder used to climb into the cab. For most units it says "Class DEP-2B" or "Class DEP-3C." Does anybody know what this means? I also noticed that the "Class DEP-3C" classification doesn't necessarily mean the unit is an F40PH-3C. 1054, the first 3C says "Class DEP-2B."

It's an old internal classification system, which follows the same format the New Haven used. "DEP" means "Diesel Electric - Passenger", and the numbers and letters after that indicate the model, generally in ascending order of when they were purchased. Per my notes from 15 years ago, the models are as follows:

1000-1017: DEP-2C
1025-1036: DEP-2D
1050-1075: DEP-2B (at least some have since been reclassified as DEP-2E)
1115-1139: DEP-3

The MP36s and HSP46's don't appear to have been given internal class numbers (there's none visible in any of my photos), but they would be DEP-4 and DEP-5 if they did.

The original F40's were classed before their 1st rebuilding:

1000-1012 Class DEP-2
1013-1017 Class DEP-2B

The FP10's were classed:

1100-1114 Class DEP-1
1150-1153 Class DEP-1S

The steam generator equipped FP10's retained their "1S" designation after conversion to 480V HEP.

Tom Coughlin
Stow, MA