Arcona

And why there is little mention about this?

The Cap Arcona was a German ship that was used as a prison ship for thousands of former prisoners of Nazi concentration camps. On May 3, 1945, it was bombed and shot by British RAF unaware civilians in the ship during an air raid on German ships on the last days of World War II. Almost 7,000 people died and 350 survived. He is known as the most favorable fire incident in history. The reason so little is known about this disaster is that the British government sealed all documents relating to the RAF to attack for 100 years (2045) embarrassment.

The possible answer lies in the fact that the U.S. military command knows about the prisoners on board, and did nothing to prevent the attack of the RAF, which took place May 3
There is also a historical fact that, according to documents at the Netherlands Institute for War Documentation (NIOD), the government of Sweden had warned the British government that the prisoners were on board ships.
In addition to this, the ship was clearly not a warship, so that the RAF attack also respond to this, especially as it was at a time when Hitler was already dead and Germany a lot of rubble.

"On May 2, 1945, the Second Army reached the city of La¼beck and Wismar. No.6 Commando, 1st Special Service Brigade commanded by Brigadier Derek Mills-Roberts and the 11th Armoured Division commanded by Major General George PB Roberts entered without La¼beck resistance. The International Red Cross has informed George Roberts PB 7000-8000 prisoners were aboard ships in the Bay of La¼beck.

Unfortunately, these things happen in war, and if we open our eyes, go right this minute, somewhere on this earth.