I've actually seen one of these guns. The Aberdeen Proving Ground museum has one (it may have since been moved to Fort Lee, but it was still at APG last year, unlike most of their collection). It had some battle damage, too. Bullet spangs and fragment scars. IIRC however, they came about when we captured the gun from the Germans. Ah, the breathless narration... H/t, Kevin.
Not bad for 1940. Remember the majority of FA remained horse-drawn. If memory serves, the US Army had begun the transition to full mech/motorized forces in 1940. The Brits went full motorized after Dunkirk (I could be mistaken, but I don't think so.) The "herrenvolk" and their allies used horses right up to the end.
My artillery unit mechanized itself in the early 20's for a exercise by using local borrowed trucks from a moving company. In a report held by the unit’s museum, the exercise showed what a drastic difference mechanization made. Mobilizing to the site was cut by a 1/3rd , manpower reduction was significant and costs for fuel was less than fodder for the horse. The report recommended that the army take a serious look at mechanization of all of the army.
Not to long ago they were renovating the parade square and when dug it up, they found the bases of the hitching posts for the horses.
I also have to wonder how well the French dealt with "shoot'n'scoot"* in terms of accuracy.
*And here I thought that was some new-fangled shock&awe concept. ;-\