German Triumph Werke Nurnberg typewriter with Rune key

This is a very old German typewriter I bought over 35 years ago at a typewriter store. We've just re-found it in the basement and are wondering if anyone knows anything else about this vintage typewriter. All the keys still work although the ribbon is a little dry. There is a serial number on the inside # 411872, additional markings on it are: Reinhold Schulz Munchen / tel. 54018 / Lindwurmstr: Perfekt: and Triumph Werke Nurnberg/A.G.Nurnberg. Additionally it has the RUNE key above the #5 key and what looks like a monogrammed "M" above the 3 key. From the research I can find on-line so far, this may be a German field typewriter. Anyone know anything about this to help me fill in the blanks about it's history??