Ardennes counteroffensive

These mortar battalions continued to support the troops of the Seventh Army as they fought to the north and northeast— the Vosges, Belfort, Bitche, Colmar were familiar names to the mortarmen. Some mortar units fired for divisions of the ist French Army which, with the U.S. Seventh, made up Lt. Gen. Jacob L. Dover s 6th Army Group. Offensive action came to a temporary halt in mid-December 1944 when the Germans launched their Ardennes counteroffensive. ... 

Preparing a 4.2-Inch Mortar Shell for Firing, Ardennes counteroffensive. 

The period of the Ardennes counteroffensive saw the start of a series of mortar shell malfunctions which were to plague the battalions for most of the winter of 1944-45. These malfunctions were of two types barrel bursts, in which the round prematurely exploded within the barrel and muzzle bursts, in which the round exploded after leaving the barrel but still within the vicinity of the mortar emplacement. 

---