This is for those that do not really know the difference or how to tell the difference. The author is getting tired of arguing about it. Also, if you have a used one that are trying to sell and the box disagrees with the following points then someone at some time put the wrong locomotive in the wrong box. The author has seen many examples of this on eBay, a RS2 in a RS1 box...etc. and therefore (of course) sold as a RS1. Email the seller about it and you'll get ,"The box says RS1".
The way to tell the difference is to look at the exhaust stack, YES, it is that easy. Look at figures 1, 2 and 3 below.
RS1
The stack is close to the cab on the fireman's side (if long nose forward). See figure 1.
Figure 1 B&O RS1 from the author's collection
RS2
The stack is on the same side of the shell but it is moved forward. See figure 2.
Figure 2 D&H RS2 from the author's collection
RS3
The stack is in the same forward position as the RS2 except it has been turned 90 degrees and placed in the center of the shell. See figure 3.
Figure 3 D&H RS3 from the author's collection
One other point is that the RS1 had a 6-539T engine while the RS2 and 3 had the 12-244 engine so the radiator intakes were different between the RS1 and the others RSs.
The author hopes this clears up the identification problem.
Addendum
Jack Shall has left a comment on the correctness of this post. Please read the comment because it describes further ways to identify the differences between the RS2 and the RS3. This comment is accurate for the prototype locomotives. However, I have not seen any differences from what I explained regarding the stack in manufacturer's models.
The Author Stands Corrected <2025-08-16>
A KATO model RS2 was found on eBay that has the turned stack in the middle of the shell, no battery box behind the engineer's position and was identified as an RS 2. See figure 4.
Figure 4 KATO RS2
If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.
Please allow me to make a small correction to your post. The RS1 indeed has the stack nearer to the cab. The RS2 you're showing has an air cooled turbocharger stack, the RS3 has the water cooled turbocharger stack. You can't use the stack to differentiate between an RS2 and an RS3 as RS3s originally came with a/c, but later came with the w/c turbos. RS2s had a/c turbos and many (most?) got converted later to w/c turbos as well. However, there is a great spotting difference. The RS2 doesn't have the large battery box on the running board behind the cab. The RS3 DOES have that box behind the cab. It is obvious in your photos. There are several other differences between the RS2 and RS3, but the battery boxes are the easiest to spot.
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