Outside the Railway Museum stands the grand electric locomotive Da 903 from 1955. With its green colouring, it is unique and has a special and rather odd history. An important role in this history is played by the locomotive models you see in the display case below.

In 1957, the well-known German toy manufacturer Märklin presented its first model railway locomotive based on a Swedish prototype. The model depicted the Da type locomotive and was designated Da 884. Like all SJ locomotives at that time, the model received a brown colour scheme (model 1).

But selling a brown model locomotive in Germany was not feasible. Electric locomotives in Germany were green, so a green version of Da 884 was simultaneously produced for the German market. Over the years, it has become a collector’s item, despite always lacking a full-scale prototype (model 2).

In preparation for the 100th anniversary of electric train operations in Sweden in 2015, the company NetRail, in collaboration with Märklin, secretly created the world's largest Märklin locomotive. Using the green model as a prototype, the full-scale Da 903 locomotive was repainted and equipped with all the model's characteristics. This full-scale locomotive stands today outside the Railway Museum.

Shortly thereafter, Märklin released an anniversary edition of the green model locomotive, now designated Da 903, derived from the full-scale locomotive (model 3).

In connection with a LEGO event at the Railway Museum, a LEGO model of the world’s largest Märklin locomotive was created in collaboration with the association Swebrick (model 4). This, in its craziness, is just as unique as the large locomotive outside.