This explains it pretty well,
http://www.landships.freeservers.com/21cm_howitzer.htm
My understanding of "munitions kolonie" is the ammunitition train for the referenced guns. This would fit in the use of the Luger as a support unit weapon.
(Here's another interesting site, has all the German military abbreviations)
http://miniatures.de/html/ger/nomenclatureG.html
rk