I believe this is the first Mercury Streamlined Passenger set offered by Marx. A 1937 catalog shows what appears to be the gray Mercury engine (it has a grille) heading up a freight consist. The M10005 had been released in 1936 so we know the car body tooling was extant. Another catalog page from 1937 shows a four piece clockwork passenger consist but it is impossible to determine whether it is gray or red. I suspect the gray sets were earliest and Marx, realizing how drab they were, changed the color schemes to red/white and copper/black (The Copper Queen) to boost sales.

The engine of this set has a switch next to the smokestack which Greenberg's Guide to Marx has incorrectly identified as being for a brass strip choo choo strip. In fact, the switch is to engage a sparkling mechanism on the front of the motor. These were not a good idea and did not last. The sparkling mechanism on a clockwork engine is adorable and practical. On an electric engine the flint is not going to last past the first day. Little boys get tired of winding up a clockwork train so the amount of playtime one sees is relatively small. Little boys will run an electric train in their sleep if allowed too! A sparkling flint in an electric train is just not going to last. It is pretty cool though when you can get the pressure just right so the engine will run and the sparkler will engage.