The song "Over There" (1917) by George M. Cohan was as well known and popular as James Montgomery Flagg's poster "I Want You." This particular version of "Over There" was sung by Nora Bayes and recorded on a 78 rpm record in 1918.
Over There

Johnnie, get your gun,
Get your gun, get your gun,
Take it on the run,
On the run, on the run.
Hear them calling, you and me,
Every son of liberty.
Hurry right away,
No delay, no delay,
Make your daddy glad
To have had such a lad.
Tell your sweetheart not pine,
To be proud her boy's in line.


Over there, over there, Send the word, send the word over there-- That the Yanks are coming, The Yanks are coming, The drums rum-tumming Ev'rywhere. So prepare, say a pray'r, Send the word, send the word to beware. We'll be over, we're coming over, And we won't come back till it's over Over there.

Johnnie, get your gun, Get your gun, get your gun, Johnnie show the Hun Who's a son of a gun. Hoist the flag and let her fly, Yankee Doodle do or die. Pack your little kit, Show your grit, do your bit. Yankee Doodle fill the ranks, From the towns and the tanks. Make your mother proud of you, And the old Red, White and Blue.

(repeat chorus twice)