On US artillery:

One of the most deadly tactics employed was the time-on-target (TOT) concentration. A TOT massed fires from several battalions onto a selected target and calculated the times of flight for the shells from each battery so that they all arrived on target at nearly the same instant (a similar tactic, called a "Stonk", had been developed independently by the Royal Artillery in North Africa).

http://www.militaryhistoryonline.com...artillery.aspx

Problems with ammunition supply did hamper efficiency at various periods. This problem reached its nadir during the fall of 1944, when the US artillery in Europe was reduced to strict rationing of ammunition. At one point, the artillery was limited to fewer than twenty 105mm rounds-per-day-per-gun. From 11 October to 7 November 1944, Third Army fired a total of 76,325 rounds of all types (an average of 2,726 per-day), which was less than the number fired on a single day during the Battle of the Bulge. Indeed, at the end of the Battle of the Bulge, ammunition reserves in the ETO were 31 percent of the War Department's planning levels (which were already conceded to be too low).

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