15th May - Holland
The Dutch forces forward of the water line fell back as planned, as the German attack was renewed now that they were able to use some of the bridges they needed. The German commander now had a problem; the time the demolitions had allowed the Dutch meant that the bulk of their forces were now manning the Water Line and the rest of the pre-war fortifications. The airborne attack had failed, with heavy losses, so the only way now was an attack against a very strong defensive position. While he had no doubt that this would work, it would take time and he would take heavy losses. The forts, inundations and river lines meant his panzers would not be effective, so it would be down to the infantry and artillery advancing on foot to do things the old-fashioned way.
Back in Berlin, High Command was annoyed the Dutch situation had not already been solved. While one part of the attack - the diversion of attention to the north and away from the Ardennes area - had been successful, the second, the elimination of Holland and the occupation of the northern Rhine crossings, had not. There seemed to be two possibilities. A methodical attack, using the units already in place, or to hold opposite the Dutch defences, keeping them there while they released some divisions for a new attack on the Dyle line, and coming back to deal with the recaltriant Dutch later.
Neither of these was particularly appealing, however a new alternative was suggested by Goering. Already angry at the defeat of his airborne attack, he offered to flatten Rotterdam. Such a devastating attack would surely cause the Dutch to surrender.
Accordingly, on the afternoon of the 15th, a large formation of over 100 He111 bombers attacked the city. By this point the Dutch fighters had been effectively wiped out in earlier actions, and only a small number were able to intercept, though they did manage to shoot down 8 bombers. The AA defences of the city accounted for a few more, but the damage was severe. The heavy use of incendiaries overwhelmed the Dutch firefighters, and a huge conflagration took over the centre of the city. While 500 people were killed, the blaze destroyed the best part of 20,000 houses.
The Dutch government were appalled at what they saw as an attack on a purely civilian target with no apparent military targets involved. There were calls for a surrender, to avoid this being repeated in other Dutch cities, but other voices pointed out that so far they had stopped the German attack, and surrendering to terror was an act of betrayal to those men who had already died stopping the Germans. This prevailed, and the Dutch were determined to fight on. There was considerable evacuation of civilians from the major urban centres, but with the Dutch troops already basically in place, this did not have the disruptive effects the Belgian refugees were causing.
Pictures of the fire and its devastating effects were quickly disseminated by the Dutch. This caused outrage in many countries, and particularly in the United States. While there had been attacks on towns and cities before, this was the first major attack purely aimed at civilians, and it marked an escalation that the Allies intended to exploit.
15th May - BEF
Sixth Army had been told that it was of the greatest importance 'to break through the enemy position between Louvain and Namur in order to prevent the French and Belgian forces establishing themselves in this position. They lost no time in trying but the British artillery was already disposed in depth and the concentration which they put down in the late afternoon caused the enemy to draw back; However at 7pm they made the first of a series of attempts to capture Louvain.
Throughout the next, May the 15th, attacks were resumed along the whole British front, the German IV Corps attacking in the 2nd Division's sector near Wavre and their XI Corps the 3rd Division in action at Louvain. Fighting began on the front of the 2nd Division during the morning, where elements of the German 31st Division made a small penetration across the Dyle in the sector held by the 6th Brigade. This was cleared up in the afternoon with a counter-attack.
A renewed attempt to take Louvain from the 3rd Division had started earlier, prefaced by a two-hour bombardment of the area north of the city held by the 9th Brigade and the 7th Guards Brigade. Here a tangle of railway lines and sidings, goods yards, sheds and warehouses made it a difficult area to preserve intact. Units of two German divisions succeeded for a time in pressing back some posts of the 2nd Royal Ulster Rifles, but a counter-attack by the 1st King's Own Scottish Borderers restored the position and drove the enemy out of the railway yards. North of Louvain the 1st Coldstream Guard were heavily attacked and their right company was for a time forced back. But here too a counter-attack in which the heavy armoured cars of the 5th Royal Inniskilling Dragoon Guards drove the enemy out and completely re-established the front. All other assaults were successfully driven off. The German Sixth Army reported to Army Group B that they had not succeeded in penetrating the Dyle defence line at any point.
In the afternoon it was learned with dismay that the French First Army on the right flank had been heavily engaged and that a 5,000-yard breach had been made in their front where there was no river protection. Lord Gort, who had established his Command Post at Lenneck St Quentin, to the west of Brussels, offered to lend General Billotte a brigade of the 48th Division, joined by one of the RTC regiments from 1st Independent Tank Brigade (both currently part of his reserve) to help in restoring the situation, as the alternative would be a withdrawal of 1st Army, which would also force the BEF to fall back so as not to leave their flank exposed.
Such action would have severely compromised the intended actions of 7th Army to seal off the German breakthrough, and the reinforcements were accepted by General Prioux. The existence of the regiment of Cutlass infantry tanks proved to be a complete surprise to the attacking infantry. While only 40 of the 48 tanks in the regiment were able to take part (due to the usual mechanical issues), the German infantry were appalled to find that their anti-tank rounds just bounced off the heavily-armoured infantry tanks. The panic this caused allowed the British force to push the German incursion back quickly, what would later be termed 'tank panic' setting in to a number of the German units. A number of attempts to stop the tanks was made by some batteries of 88mm guns, but while these succeeded in killing a few of the tanks, the advancing regiment covered their advance with smoke and then destroyed the guns with a combination of their own supporting artillery and HE rounds from the tanks, before driving over them and carrying on. By the evening, the breach had been sealed, and the 1st Army position on the Dyle line restored.
(In OTL the tanks weren't available, and Prioux refused the aid of a single brigade, starting the general falling back and retreat from the Dyle. Here he has hopes for the tanks, and also Billotte's actions with 7th Army has made him try and hold for longer)