This inscription seems to be incomplete and misspelled.
“3rd Group (and?) ---- Machinegun.”
A word or two might be washed out between 3rd Group and Machinegun. Whatever the case, machinegun is misspelled. The actual spelling of machinegun in German is “Maschinengewehr.” It appears as if someone was practicing their language skills as “Machine” is written in English and “Gun” is in German (Gewehr).