...The car with the silver tanks is a helium car. It was actually a very rare car in real life service but, for some reason, caught the fancy of model railroaders. They have been made in almost every scale by AHM, Ambroid, and Roco, for Atlas, among others. They were originally all built for the Navy to refuel blimps. In the mid 50's the Navy was mostly out of the lighter than air business and the remaining cars were split up between the Bureau of mines and the Atomic Energy Commision. The AEC used helium in some experimental reactors and the Bureau of Mines used a helium/oxygen mixture for self contained breathing apparatus for mine rescue teams. The Bureau of Mines cars lasted the longest, with some in service until the mid-90's but most of the approximately 300 cars ever built were scrapped after the Navy got out of the blimp business in 1962. A few have been preserved in museums but there are none in active service now.