This very nice, and rare, 3-rail AC HO gauge locomotive by Marklin is 3111 a Bavarian S3/6 steam loco in brown (or perhaps more maroon) SNCB livery. It has running number 5920.  

The steam locomotives of the class S 3/6 of the Royal Bavarian State Railways were express train locomotives with a four-cylinder compound engine . The wheel arrangement is 2'C1', also known as Pacific. 

These locomotives are notable among the state railway locomotives in that they were procured over a period of almost 25 years, even during the days of the Deutsche Reichsbahn. A total of 159 examples were made, more than all other state railroad Pacifics combined. 89 of the locomotives (series a to i) were procured by the Bavarian State Railway and 70 (series k to o) by the Deutsche Reichsbahn.

In the 1950s, the Deutsche Bundesbahn modernized a large part of its vehicle fleet. 30 units of the 18 5 series were also converted by the companies Krauss-Maffei and Henschel . These were series l to o locomotives procured by the Reichsbahn between 1927 and 1930.

The converted locomotives were given the new road numbers 18 601-630 and were used in express train service, where their performance almost matched that of the 01 series . They were stationed in the depots in Darmstadt, Hof , Regensburg, Nuremberg Hbf , Lindau and Ulm.

The last locomotives (18 622 and 18 630) were decommissioned in Lindau in 1965 and scrapped from 1966 onwards. 

A number remain in preservation including 18 451.

In 1919 three Bavarian S 3/6 locomotives were assigned to Belgium, which were intended for pulling express trains. These three locomotives were sold to the Belgian State Railways (Chemins de fer de l'État Belge) in 1920. These were the Bavarian locomotives 3620, 3646 and 3649, which were delivered to the Bavarian K.Bay.Sts.B. in 1918. had been delivered.

At the Belgian State Railways they were classified as type 59 with the company numbers 5920, 5946 and 5949. The locomotives classified as Type 59 were initially stationed in Brussels North where they were used together with the Type 61 (Prussian S 10.1) locomotives, among others. to pull heavy express trains to Ostend and Herbesthal. In 1922 the locomotives were stationed in Ostend, but stood idle there. In the same year they were stationed in Tournai where they were deployed to Brussels and Lille (Belgium). The locomotives were only in active service for a short period with the Belgian Railways and in 1923 all three were retired. The locomotives were scrapped in 1924.

This Era Ith version of the NMBS/SNCB is actually a fantasy version, as these Type 59 locomotives never ran in this brown livery, but had the original green colour of the K.Bay.Sts.E until their scrapping in 1924.

The loco is in good condition as you can see in the pictures, We are unable to test it as we do not have a three rail AC test rig or track, so we have not tested it but can see no reason why it would not run. It is sold in untested condition, this means that it may not run, and as such it is not being sold in running condition. However a complete external visual inspection has shown no reason why this loco would not run and the overall condition is very good. The box is in good if slightly shelf worn condition. 

Overall this is a really nice scale locomotive and would look fantastic on a layout.

Do please have a look at my other listings, I typically have various HO and OO locos on offer as well as an extensive range of imported N gauge locos and other items. 

Note: I do recommend all locos are cleaned & serviced, as they have some age to them even if the quality looks at the highest level (fairly standard advice for all locos!).