This might explain it somewhat:
"Reichsführer SS Heinrich Himmler had issued the secret order to all concentration camp commanders that surrender was unacceptable, that concentration camps were to be immediately evacuated and no prisoner was to fall into the hands of the enemy alive. Himmler intended that all prisoners were to be killed. In the Neuengammer concentration camp the order was received by SS-Obersturmführer Karl Totzauer, adjutant to the commander Max Pauly. This order started the death marches from Neuengamme, the largest concentration camp in Germany, with its 96 satellite camps, of which more than 20 were women's camps. The SS drove the prisoners northwards, sometimes aimlessly, on foot or by train, without food or drink. Hundreds died of hunger or thirst or were shot where they fell being too exhausted to continue. Neuengammer satellite camp Hannover-Stöcken was initially evacuated by rail to Bergen-Belsen but then diverted towards Berlin, Bergen-Belsen being over full. After three days the remaining prisoners were detrained at Mieste and made to march to Gardelegen army camp, and two days later to the village of Isenschnibble on the outskirts of Gardelegen. Here they were murdered. NSDAP district commander Gerhard Thiele had prepared a death trap. Following his explanation that the prisoners were to be removed from the war zone and Gardelegen defended against the advancing American troops the remaining 1,038 prisoners were driven into the large village barn. The SS had poured petrol and oil over the straw. SS-Scharführer Braun then threw a burning torch through the door and the SS men immediately began shooting at all four closed barn doors. Those who crawled under the side walls were shot. 1,016 people were murdered, 22 escaped.
As the death marches advanced northwards Hamburg regional commander Karl Kaufmann sought ships in which to put the concentration camp prisoners to sea. The few remaining ships, including ferries and lighters, were deployed in the East rescuing civilians and retreating German troops fleeing the advancing Russian army. As Commissionary for Defence of North Germany and Reich Commissionary for Merchant Shipping he had the right of disposal of all non-military shipping. Being informed about the Cap Arcona he ordered the prisoner transports from Neuengamme concentration camp and its satellite camps to be directed to Lübeck and the prisoners embarked. 11,000 prisoners arrived at Lübeck quayside. Lübeck had suffered severe bomb damage. The first Neuengamme concentration camp prisoners arrived in cattle-waggons at Lübeck harbour on 19 April 1945. Between the 19th and the 26th April new transports arrived. Roughly 50 percent of all prisoners did not survive the journey.
On the 17th April 1945 the Thielbek was informed that they were to make ready for a special operation. On the 18th April, SS men came aboard and captain John Jacobsen of the Thielbek and Captain Bertram of the Cap Arcona were called to a conference. Captain Jacobsen returned to inform his crew that they had been ordered to take concentration camp prisoners on board. Both he and captain Bertram had refused. The following day Jacobsen returned defeated having lost command of his own ship. Shortly thereafter the first train arrived. Provisional toilets were installed on the deck of the Thielbek and embarkation started on the 20th April. The Swedish Red Cross were present and all concentration camp prisoners except the Russian prisoners received a food parcel which, with the combination of malnutrician and thirst, caused terrible suffering. The water supplied from the ship's tank was totally insufficient. Twenty to thirty prisoners died daily and were removed by lorry. All prisoners, except the political prisoners, remained one or two days on board before being transferred to the Cap Arcona by the Athen. The SS personnel were gradually reduced and replaced by 55 to 60 year old territorial army members and marines. There was straw on deck for the holds there being no beds. There were large stocks of provisions under tarpaulin on deck but distribution was disorganized. The sick and the Russian prisoners received little. The latrines were inadequate. Buckets were lowered into the holds and raised when full. The stench was terrible. Gastroenteritis raged.
On the morning of the 20th April 1945 SS-Sturmbannführer Christoph-Heinz Gehrig, head of administration at Neuengamme concentration camp was sent to Lübeck by Commandant Max Pauly. Gehrig had been responsible for the murder of the twenty Jewish children at the Janusz-Korczak-School at 92 Bullenhuser Damm in the Hamburg district of Rothenburgsort. They had been used for tuberculosis experiments in Neuengamme concentration camp. Gehrig was to escort the prisoners to their deaths aboard the Cap Arcona. He ordered captain Nobmann of the Athen to take 2,300 prisoners and 280 SS guards on board and to ferry them to the Cap Arcona. Captain Nobmann initially refused but obeyed when threatened with being shot following a drumhead court martial. The SS and Kapos drove the prisoners on board with yells and blows. They had to climb down rope ladders into the deep holds of the ship. In the haste many prisoners fell and were seriously injured. There was hardly room to move in the dark, cold and damp holds. There were no toilets or water. After some hours the fully laden ship left the harbour for the Cap Arcona anchored off Neustadt. Captain Bertram refused to take the prisoners on board even after the SS came aboard. The Athen remained off Neustadt overnight and returned to Lübeck next morning, the 21st April, the prisoners having been given nothing to eat or drink.
SS-Sturmbannführer Gehrig informed camp commander Pauly of captain Bertram's refusal to take prisoners on board and Pauly informed Head of Gestapo Graf Bassewitz-Behr who reported to Gauleiter Kaufmann. On the evening of the 21st April Kaufmann sent his personal advisor SS-Hauptsturmführer Horn to John Eggert, chairman of the board of directors of the Hamburg-Süd shipping line to inform him that Captain Bertram was to follow the SS order to take prisoners on board or be shot. Eggert telephoned Bertram who in turn called Admiral Engelhardt head of naval transport. It was clear to all that the Cap Arcona was to be scuttled with the prisoners on board. Engelhardt sent captain Rössing to Kaufmann to lodge the navy's formal protest against the impounding of the Cap Arcona but he only got as far as SS-Hauptsturmführer Horn who ordered Lieutenant-Commander Lewinski and SS-Sturmbannführer Gehrig to impound the ship with force of arms. In the meantime five days had passed and on the 26th April Lewinski and Gehrig met in Lübeck and travelled to Neustadt together from where they were ferried to the Cap Arcona with a motorboat from the U-boat school, escorted by an armed SS commando. Captain Bertram unsuccessfully attempted to negotiate with Lewinski and Gehrig. He was given the ultimation: either immediately give permission for the Athen to moor alongside and transfer its prisoners to the Cap Arcona or be shot without a court martial. Bertram capitulated. Before the Athen moored alongside a second time a launch brought SS men under SS-Untersturmführer Kirstein who removed all life belts and jackets and all benches which could be used as rafts and locked them in the storage room.
On the 27th April the Athen arrived in Neustadt with 2,500 prisoners from Mittelbau-Dora concentration camp who were transferred to the Cap Arcona. For three days the Athen journeyed to and fro between Lübeck harbour and the Cap Arcona. There were finally 6,500 prisoners on board and 600 SS guards. There was hardly anything to eat or drink and prisoners continued to die. A launch brought drinking water and took the dead back to Neustadt daily. The Russians received the worst treatment being locked in the lowest hold without fresh air, light or food. The number of dead grew ever larger. The Athen made its last journey to the Cap Arcona on the 30th April but this time to take prisoners off as the Cap Arcona was so over crowded that even the SS could no longer endure the starvation, stench and dead."