VACANT REGIMENT. German regiments (or battalions) were so called when the colonel by whose name they had been known was no longer in command. Baurmeister, for example, refers in a letter of 2 June 1777 to "the Regiment vacant Rail." The latter unit was commanded in turn by Rall, Woellwarth, Trumbach, and d'Angelli; it was a "vacant regiment" during the intervening periods.
"Vacant Regiment." Encyclopedia of the American Revolution: Library of Military History. . Encyclopedia.com. (September 23, 2018). http://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/vacant-regiment
"Vacant Regiment." Encyclopedia of the American Revolution: Library of Military History. . Retrieved September 23, 2018 from Encyclopedia.com: http://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/vacant-regiment