This s a song brought back from World War II by my father (although the song is far older than that with roots in the British Royal Artillery). It is a song, much like "The Twelve Days of Christmas", or "Old MacDonald’s Farm", or "There was an old lady who swallowed a fly" in which a list is added to, one item st a time, making the list longer and longer. In this case military ranks starting with privates; then corporals and privates; then sergeants, corporals and privates; etc., until one runs the entire gamut of the army: generals, colonels, majors, captains, shavetails (lieutenants), sergeants, corporals, and finally privates. It was a song used as a cadence while marching, and also in bars while drinking! It is a fun song used at gathering of military types, actives or veterans. BTW, "shavetails" used for lieutenants is in reference to cavalry horses. Young, inexperienced, lieutenants are compared with young, inexperienced, and unreliable horses (who seem to cause more trouble than they are worth!) that had their tales shaved (clipped short) so one could recognize these horses (and hopefully have them assigned to another rider!).