The more than 600 black men killed when the SS Mendi sank, died believing their contribution to World War I would lead to the better treatment of blacks in South Africa, President Jacob Zuma said on Tuesday.

"Today, we restore the dignity and humanity of the black soldiers who perished on that fateful day," he said at the Armed Forces Day celebrations in Durban.

"We salute their quest for a more equal, and just world, for the better world we are still working to achieve 100 years later."

Tuesday marked 100 years since the SS Mendi sank. The British government had chartered it as a troop carrier. On February 21, 1917, it was carrying 823 members of the fifth battalion. They had completed 34 days of the voyage from Cape Town to England, and were on their way to France.

A much bigger ship, the SS Darro, which was bound for Argentina, collided with the SS Mendi in the English channel, almost cutting it in half, Zuma said.

A total of 660 South Africans died in the disaster, mostly black South Africans.

"Black people had volunteered to join the First World War in order to fight against fascism. They were ahead of their time. They were internationalists who loved peace and justice.

"They also joined the war, believing that their contribution would lead to better treatment back home after the war by the colonial masters."

They were not allowed to carry weapons and were meant to work as labourers, rather than as fighting soldiers. They were never decorated or awarded any medals at the end of the war.

The country’s history was one of "brutal and blatant racism and colonialism".

Zuma said the sinking of the SS Mendi was a tragedy second only in scale to the tragedy at Delville Wood, France, in 1916. A South African delegation visited France last year to pay tribute to those soldiers killed there.

A new monument in France honoured all South African soldiers, black and white, Zuma said.

In recognition of the SS Mendi tragedy, one of the country’s national orders includes the Order of Mendi for Bravery.