It has been proved that two gassing operations took place at the Neuengamme camp near Hamburg. On both occasions Soviet prisoners of war from Fallingbostel POW camp in the Lüneburg Heath were brought to Neuengamme, and were killed as soon as they arrived. There were 193 men in the first convoy, in September 1942, and 251 in the second, in November of the same year.
At Neuengamme there were no gas chambers, properly speaking. What was known as "the bunker" was used: it served as the camp prison, and it was there that executions by shooting usually took place. It was made gastight, and new doors were installed, along with a system of heating pipes that served for distributing the gas and for ventilation.SS-Unterscharführer
Willi Bahr, a noncommissioned officer from the sanitation service, had been trained in the use of Zyklon B. When the British military government brought the SS members of the camp staff to trial, he took the stand in his own defense. This is how he answered the defense lawyer's questions:
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Lawyer: Now let's go on to the gassings.
Witness: They took place in the autumn of 1942.
L.: How many victims were there?
W.: Between 180 and two hundred, approximately.
L.: Had some changes not been made in the bunker in the autumn of 1942?
W.: I saw these changes once they have been completed, but that's all I can say.
L.: What did they consist of, essentially?
W.: A pipe was installed on the roof, and a hot-air device with an electric
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coil. I wondered what could be done with that, because I didn't yet know anything about what was going on.
L.: It was then that a convoy arrived. What sort of convoy was it?
W.: A convoy of Russians.
L.: Were they mostly officers?
W.: I don't know anything about that.
L.: Did you see these Russians when they were brought into the camp?
W.: No. I saw them only when they were being taken to the bunker.
L.: Who was the garrison doctor?
W.: Dr. von Bothmann. He gave us quite a lecture: we had to gas these Russians the same day. He ordered us to do it. Whereupon I repeated: "It's a thing I can't do." For the second time, I was threatened with an SS police court. I carried out the order so as not to bring misfortune on my family.
L.: Why had you been assigned to this job?
W.: Because I had taken the health-service course in Berlin and because I worked in the camp hospital. One of the members of the hospital health service had to do it.
L.: Yet you said that you knew Zyklon B only as a means of controlling pests?
L.: And not as a way of killing human beings by asphyxiation?
W.: All of that had already been discussed between the garrison doctor and the camp commandant.
L.: Didn't you need more precise instructions as to the details of what you had to do?
W.: The garrison doctor and the top camp officials were all around and said what had to be done.
L.: How did you get the gas? Was it you who were in charge of storing it?
W.: It was kept in the dissecting room.
L.: Who was responsible for it?
W.: Kapo Müller, of the delousing station.
L.: So whom did you apply to?
W.: I may have asked Kapo Müller if he had any.
L.: Did he have enough?
W.: Yes. I needed only five cans.
L.: Did you know that that would be enough?
W.: Yes. The delousing-station doctor had ordered me to pour in half a can per pipe.
L.: So then you approached the bunker with the cans?
W.: No. It was the prisoner Müller who did that.
L.: So you were already near the bunker?
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L.: Did you see the Russians when they were taken to the bunker?
W.: Yes. They were undressed and were being taken from the baths to the bunker.
L.: Did the Russians know what was in store for them?
W.: I have no idea.
L.: Did the Russians follow along without difficulty or did they resist?
W.: I couldn't form an opinion about that.
L.: When we visited the premises, we saw that the cells of this bunker were very narrow. The bunker must have been very full if 180 to two hundred people were put inside.
W.: I can say nothing about that question because I never worked at that. That was done by the Blockführers. My job was limited to preparing the Zyklon B to put into the pipes.
L.: Were there many SS members present?
W.: All the top camp officials were standing around, the head doctor, the camp doctor, the head of the camp, the Rapportführer, and others.
L.: Was it the head doctor, von Bothmann, who directed the whole operation?
L.: So Müller approached the bunker with the Zyklon B : What did you do then?
W.: At the same time as Bünning, I had climbed up onto the roof with a ladder.
L.: Did you already have the Zyklon B with you?
W.: No. Müller opened the cans on the ground, and another prisoner passed them up to me.
L.: Weren't there any precautions to be taken when the cans were opened?
W.: Yes. A rubber cap was immediately placed over the opening.
L.: I mean, was it dangerous for the person who was doing the opening?
L.: Were you wearing a gas mask?
W.: Yes. Everybody was wearing a gas mask.
L.: I imagine that Zyklon B comes in crystals?
W.: Yes. It looks like calcium carbide.
L.: So, standing on the roof, you were handed these opened cans. What did you do then?
W.: We poured half a can into each pipe.
L.: You said "we." Who was with you?
W.: Bünning. Then Dr. von Bothmann ordered us to leave and not to
come back until two hours later, because the bunker wouldn't be opened before then.
L.: Was the bunker guarded during all that time?
W.: I couldn't say. The Blockführer or the prisoner-block leader most likely stayed there.
L.: When did the operation begin?
W.: A little before midday or a little after. I can't say exactly.
L.: Did you go back two hours later?
W.: Yes. Bünning and I went back to the bunker.
L.: What happened then?
W.: When we got there, the bunker had already been opened by the Rapportführer.
L.: Were the cell doors already open too?
W.: They hadn't been closed at all, only the doors of the bunker.
L.: What did you see?
W.: Some corpses had already fallen outside. It was a frightful sight.
L.: Where were the corpses taken?
W.: Bünning and I were supposed to take them to the crematorium. After the first cart had been unloaded, the head doctor came up and said we didn't have to do that job.
L.: So the operation was finished, where you were concerned?
W.: Yes. 
A very large majority of the second convoy of Soviet captives brought from Fallingbostel to Neuengamme was made up of men who had been mutilated in the war. Prisoners in the Neuengamme camp saw how they had to take off their prostheses first and how, after having done so, they were pushed naked into the bunker.