They were odd looking contraptions built for a specific reason but the camelbacks or "Mother Hubbards" certainly were a unique locomotive. While most locomotives had their cabs in the back of the boiler, the camelback was developed to burn anthracite coal and was primarily found in the eastern Pennsylvania area. They were much more common in the early 1900s and were more popular during that time but some of them remained in service well into the 1930s. The Reading & the Central of New Jersey were two lines that made extensive use of the camelback design.
Anthracite coal was plentiful in that region of the country but it had different burning characteristics and required a much larger firebox to provide the heat necessary to provide sufficient steam to power the locomotive. While some locomotive builders did incorporate a cab at the rear of the boiler, this proved to be a problem for the loco's operation, especially from a visibility standpoint. So the cab was moved to the middle of the engine and the design was rather successful in meeting its purpose.
There was one major problem though... the fireman was stationed on the back of the locomotive, out in the elements while the engineer was in the relative warmth & comfort of the cab astride the boiler. There are stories of firemen who just flat-out quit, leaving the locomotive stranded out in the middle of nowhere when the cold, rain, ice & snow became too much for them to handle. But that is not to say that the engineer didn't have problems as well. There were times that the locomotive side rod would break and the broken rod would go "around the clock," crashing up through the floor of the cab with often fatal consequences.
At one time, the Wheeling & Lake Erie, a road not located in the eastern Pennsylvania area, acquired three camelbacks to serve their line. It was believed that they were experiencing a power shortage and were willing to take anything that was available. When anthracite coal became too hard and too expensive to obtain, the road rebuilt the locomotives into a more traditional configuration with the cab at the rear. Those locos went on to be recognized as some of the best steaming locomotives on the line. This was probably due to the larger firebox configuration.
Because of their appropriateness for a specific region of the country, camelbacks would not necessarily be at home on most any railroad. I'm not aware of any camelback locos that are currently being mass-produced. Some are available in brass and you might still find some of the old Mantua camelback locos on Ebay. IHC also had one in production for a perieod of time. They aren't too hard to kitbash if you are really interested. But the other side of the coin is as I have always said: "It's your railroad, do what you want!" The camels certainly were unique beasts; among some of the most unusual sights along the right of way...