Originally Posted by Jazsa
Would 100 barrels blanket a 1000m x 100m rectangle that would cover each landing beach? ...
No. To continue with the example of Omaha Beach the landings were occuring across a 7,800 meter front with a nominal depth of 300 meters. So 2,340,000 square meters to cover. If your 15cm ammunition has a effective casualty radius of 30 meters thats 2800 square meters so to cover the entire beach with the ECR of one volley would require 835 rounds. If I recall correctly the unit of fire for 15cm ammunition for a German howitzer would have been 40 rounds. Ordinarily a German inf div had 12 15 cm field howitzers & six 15cm infantry guns in the regimental cannon companies. At a sustained RoF of 2-3 per minute those 18 cannon can scatter their basic load of 720 rounds across the beach in <20 minutes. If my math is correct thats about 2.14 % of the beach per minute. That is a very light bombardment barely qualifying as harrassing fires.
The trick was the Germans were short of all classes of artillery, even counting obsolete cannon. The 352 was actually lucky to have a full complement of good quality modern Cezch cannon, even if they were all 10cm caliber. The static divisions were stuck with a lot of light & obsolete cannon in calibers ranging from 7cm to 8.5, or 10cm; shooting antiquated ammunition, and in 25% to 50% of a usual infantry divisions complement.
The artillery fires were supplemented with a variety of rocket batteries. These 'werfer' style launchers seem to have been one or two shot affairs. & each infantry battalion had 4-6 mortars to add to the harrassment.
I dont have all the details of how the German artillery commander of the 352 ID used his weapons. One fact is the priority of fire for the artillery was on the landing craft at the waters edge. A lot of them were hit by artillery fires during the day. Mortars and other weapons seem to have been the bulk of the fires covering the Resistance Nests or strong points.
Another fact is the defending artillery was still firing through the afternoon. so, either the commander was being miserly with the ammo, or the delivery of more ammo was effected. Perhaps both.
Fact three: German artillery doctrine emphasized accuracy over volume. A policy dictated by a chronic ammo shortage. So, I suspect the artillery attacking OMAHA beach was carefully and methodically attacking each target with a small number of rounds, & the commanders/observers were carefully picking the targets.
Somewhere I have laid out a calculation for the volume of artillery fire needed to properly suppress O beach around 07:00 or 08:00 6th June. Your idea may not be far off in terms of ammunition required. The trick is the Germans did not have 500 15cm howitzers in all of Normandy that morning. They may not have had even 100.