It is indeed the folk song "Musketier' sind lust'ge Brüder" (also known as "Siegreich woll'n wir Frankreich schlagen"), cut from Gustav Gnauck's march "Soldatenmut", a recording from 1940 by Hans Teichmann's band. It's the 2nd strophe: "Unser Hauptmann steigt zu Pferde, führt uns in das Feld. Siegreich woll'n wir Frankreich schlagen, sterben als ein tapfrer Held."
Being tied to the Franco-Prussian war (1870), the old "Musketier' sind lust'ge Brüder" song was repopularised during the invasion of France (1940). Composer Herms Niel used its melody in two of his war campaign songs: as closing tune in "Kamerad, wir marschieren im Westen!" (Frankreichlied) and as trio in "Gegen Briten und Franzosen" (Marsch nach der Melodie: Siegreich woll'n wir Frankreich schlagen). Teichmann's band recorded the old Gnauck's and the new Niel's compositions in one recording session, dedicated to the invasion of France.
As I wrote before - war and propaganda songs are not just music, as ignorant people often like to "think" and claim. There's much symbolism and hidden messages in them, above all the reminders of past conflicts with a certain nation, whose purpose is to reawake old enmity and hatred.
Over to Teppeny!