German bombing of Rotterdam

In 1940, Rotterdam was subjected to heavy aerial bombardment by the Luftwaffe during the German invasion of the Netherlands during the Second World War. The objective was to support the German troops fighting in the city, break Dutch resistance and force the Dutch army to surrender. Bombing began at the outset of hostilities on 10 May and culminated with the destruction of the entire historic city centre on 14 May, an event sometimes referred to as the Rotterdam Blitz. According to an official list published in 2022, at least 1,150 people were killed, with 711 deaths in the 14 May bombing alone, and 85,000 more were left homeless.
The psychological and the physical success of the raid, from the German perspective, led the Oberkommando der Luftwaffe to threaten to destroy the city of Utrecht if the Dutch command did not surrender. The Dutch surrendered in the late afternoon of 14 May and signed the capitulation early the next morning.

Prelude

The strategic location of the Netherlands between the United Kingdom and Germany made it ideal for the basing of German air and naval forces to be used in attacks on the British Isles. The Netherlands had firmly opted for neutrality throughout the First World War and had planned to do the same during the Second World War. It had refused armaments from France and made the case that it wanted no association with either side. Armament production was slightly increased after the German invasion of Denmark and Norway in April 1940, but the Netherlands had only 35 modern wheeled armoured fighting vehicles, five tracked armoured fighting vehicles, 135 aircraft, and 280,000 soldiers, and Germany committed 159 tanks, 1,200 modern aircraft, and around 150,000 soldiers to the Dutch theatre alone.
With a significant military advantage, the German leadership intended to expedite the conquest of the country by first taking control of key military and strategic targets, such as airfields, bridges, and roads, and then using them to gain control of the remainder of the country. The first German plans to invade the Netherlands were articulated on 9 October 1939, when Hitler ordered, "Preparations should be made for offensive action on the northern flank of the Western Front crossing the area of Luxembourg, Belgium, and the Netherlands." The attack was to be carried out as quickly and as forcefully as possible. Hitler ordered German intelligence officers to capture Dutch Army uniforms and to use them to gain detailed information on Dutch defensive preparations.
The Wehrmacht launched its invasion of the Netherlands in the early hours of 10 May 1940. The attack started with the Luftwaffe crossing through Dutch airspace and giving the impression that Britain was the ultimate target. Instead, the aircraft turned around over the North Sea and returned to attack from the west and drop paratroopers at Valkenburg and Ockenburg Airfields, near the seat of government and Royal Palace in the Hague, starting the Battle for the Hague. Germany had planned to take control swiftly by using that strategy, but the assault on The Hague failed. However, bridges were taken at Moerdijk, Dordrecht and Rotterdam, which allowed armoured forces to enter the core region of "Fortress Holland" on 13 May.

Battle for Rotterdam

The situation in Rotterdam on the morning of 13 May 1940 was a stalemate as it had been over the previous three days. Dutch garrison forces under Colonel P.W. Scharroo held the north bank of the Nieuwe Maas river, which runs through the city and prevented the Germans from crossing; German forces included airlanding and airborne forces of General Kurt Student and newly-arrived ground forces under General Schmidt, based on the 9th Panzer Division and the Leibstandarte Adolf Hitler, a motorized SS regiment. A portion of the 16th Air Landing Regiment that had landed outside the city had managed to fight their way into the city and capture key bridges, but they were soon surrounded and in danger of being overrun by Dutch attacks on their pocket. Outnumbered, with their numbers being reduced by casualties and ammunition running out, things were becoming desperate for the surrounded German paratroops.
A Dutch counterattack led by a Dutch marine company had failed to recapture the Willemsbrug traffic bridge, the key crossing. Several efforts by the Dutch Army Aviation Brigade to destroy the bridge also failed.
General Schmidt had planned a combined assault the next day, 14 May, using tanks of the 9th Panzer supported by flame throwers, SS troops and combat engineers. The airlanding troops were to make an amphibious crossing of the river upstream and then a flank attack through the Kralingen district. The attack was to be preceded by artillery bombardment, while Gen. Schmidt had requested the support of the Luftwaffe in the form of a Gruppe of Junkers Ju 87 dive-bombers, specifically for a precision raid.
Schmidt's request for air support reached the staff of Luftflotte 2 in Berlin. Instead of a precision bombing, a carpet bombing by Heinkel He 111 bombers was carried out, with only a Gruppe of Stukas focusing on some strategic targets. The carpet bombing had been ordered by Hermann Göring, specifically to force a Dutch national capitulation.

Negotiations

The bombing was initially scheduled for 13 May, but low clouds made targeting impossible and the raid was postponed until the following day. At roughly 10:30 on 14 May, General Rudolf Schmidt issued an ultimatum to the Dutch commander, Colonel Scharroo:

To the Commander of Rotterdam
To the Mayor and aldermen and the Governmental Authorities of Rotterdam
The continuing opposition to the offensive of German troops in the open city of Rotterdam forces me to take appropriate measures should this resistance not be ceased immediately. This may well result in the complete destruction of the city. I petition you – as a man of responsibility – to endeavour everything within your powers to prevent the town of having to bear such a huge price. As a token of agreement I request you to send us an authorised negotiator by return. Should within two hours after the hand-over of this ultimatum no official reply be received, I will be forced to execute the most extreme measures of destruction.
The commander of the German troops.

The Mayor of Rotterdam, Pieter Oud, consulted with his aldermen and concluded that there was not enough time to evacuate the city within the two-hour period the Germans had set. Mayor Oud pleaded with Scharroo to surrender. However, Scharroo was not happy with the integrity of the letter as it had not been signed by anyone on the German side; therefore, he refused to seriously consider the surrender and instead replied asking for further details:

To the commander of the German troops.
I am in receipt of your letter. Subject letter has not been duly signed and did not mention name and rank of its originator. Prior to seriously considering your proposal, the letter should be duly signed and mention your name and rank.
Colonel, commander of the Dutch troops in Rotterdam, P.W. Scharroo

On receipt of Scharroo's letter, Schmidt sent a telegram to the 2nd Luftflotte stating:

Airstrike postponed due to ongoing negotiations. Return to stand-by status.

It had been arranged that the Wehrmacht would shoot red flares into the sky if negotiations had begun, signalling the bombers to turn back. However, two groups of Heinkel He 111 bombers were approaching the city: 36 from the south and 54 from the northeast, which was still held by the Dutch. The smaller bombing group in the south saw the flares and most of its planes turned back, but the larger group proceeded to destroy the city. General Schmidt exclaimed, "My God, this is a catastrophe!"

Bombing

In total, 1,150 50-kilogram and 158 250-kilogram bombs were dropped on the city, mainly in the residential areas of Kralingen and the medieval city centre. Most of them struck buildings, which immediately went up in flames. The fires across the city centre spread uncontrollably and, in the subsequent days, were aggravated as the wind grew stronger; they merged to become a firestorm. Reports stated that 900 people had reported been killed and of the city centre had been destroyed. 24,978 homes, 24 churches, 2,320 stores, 775 warehouses, and 62 schools were destroyed.
50 kilometres away in Utrecht, Cornelia Fuykschot described the aftermath:

…a haze began to cover the western sky, and as the sun had passed the zenith and moved westward, it grew redder and redder, until it finally hung there as a glowing red ball in the midst of a dark grey sky. One could easily look at it with the naked eye now, it was more like a moon, except that the deep red began to turn almost brown. As the haze came nearer, it turned the glorious spring day into a gloomy mid-November darkness, and as we stood there gazing at the sky and not understanding what was happening, a flake of paper came down, and another one, and more…. Some were charred, around the edges, some had flowers on them like wallpaper, others print. Where were they from? Was there a fire somewhere? If so, it had to be a gigantic fire to blacken the sky like this.

Schmidt sent a conciliatory message to the Dutch commander General Winkelman, who surrendered shortly afterwards at Rijsoord, a village southeast of Rotterdam. The school where the Dutch capitulated was later turned into a small museum.

Responsibility

The telegraphed message from Schmidt to halt the bombers and put them on standby was confirmed as received by the 2nd Luftflotte at 12:42. The commander of Luftflotte 2, Field Marshal Albert Kesselring was interviewed about the event during the Nuremberg Trials by Leon Goldensohn, who recalled:

Kesselring admitted that the conditions were such that an attack could have been called off, but still clung, rather unreasonably, to the idea that it was tactically indicated because he had been ordered to do so, and he was not a politician but a soldier

Kesselring stated that he had not known about the capitulation, but that is contradicted by the evidence that his headquarters had received the message at 12:42, roughly 40 minutes before the bombs started to fall. Yet, at Nuremberg, both Göring and Kesselring of the Luftwaffe defended the bombing on the grounds that Rotterdam was not an open city but one stoutly defended by the Dutch. That said, it would be unreasonable for the Germans to bomb a captured city as that would mean it was occupied by their own troops. In his memoirs, written while he was in prison for war crimes, Kesselring gave his account:

On the morning of 13 May, Student kept calling for bomber support against enemy strongpoints inside Rotterdam and the point of main effort at the bridges where the parachutists were held up. At 14:00 hours the sortie in question was flown, and its success finally led to the capitulation of Holland on 14 May 1940

General Student had requested strikes against enemy strongpoints, not carpet-bombing of the city. Had the Germans indiscriminately carpet bombed the city, they would have endangered their own troops holding out around the bridges. Kesselring also states in his memoirs that he spent hours in heated argument with Göring on how the attacks were to be carried out, if at all. The arguments happened before the bombers took off and so that cannot be used as an excuse for why he did not get in contact with the bombers.
The fact was that he had already admitted at Nuremberg that he was for the attack since he wanted "to present a firm attitude and secure an immediate peace" or take "severe measures". Kesselring further states:

As a result I repeatedly warned the bomber wing-commander to pay particular attention to the flares and signals displayed in the battle area and to keep in constant wireless contact with the Air-landing Group.

With that in mind, it is unlikely that the bombers would have reeled in their antennas until a few minutes before releasing their bombs. The argument that the antennas were reeled in is contradicted also by the fact that Kesselring quotes Oberst Läckner in his memoirs:

Shortly before the take-off a message came through from Air command saying that Student had called upon Rotterdam to surrender and ordering us to attack an alternative target in case Rotterdam should have surrendered in the meantime ― Oberst Läckner

That invalidates the argument that the bombers had reeled in their antennas because the bombers had not taken off. That indicates that Kesselring must have made the decision to attack Rotterdam regardless of the negotiations.