Original Finnish enameled steel field mug.
This type of white enameled steel mug with blue rim and black flat handle can be seen a lot in period photographs from the front. These were most likely issued instead of the army model aluminium field mug to keep up with demand. These mugs were manufactured by the largest steelworks in Finland: Wärtsilä-yhtymä Oy.
The enamel is in great condition, although there are small enamel chips on the edge. Overall a good and usable mug.
See the photos for details.