An unknown donor left the bell, wrapped in plastic, at Swanage Pier in the town of Swanage on the Dorset coast in the early hours of Wednesday morning, having alerted BBC reporter Steve Humphrey.
The caller is reported to have said the recent coverage of the Mendi centenary had prompted him to hand over the artefact. It bears the name “Mendi” on its side.
A note under the plastic wrapping read: “If I handed it in myself it might not go to the rightful place. This needs to be sorted out before I pass away as it could get lost.”
The BBC report on the find suggests that the bell “is thought to have been stripped from the wreck by divers”. The wreck was located on the seabed 11 nautical miles (20km) south west of St Catherine’s Point on the Isle of Wight in 1945, and positively identified in 1974.
The report quotes maritime archaeologist John Gribble, who has surveyed the ship, as saying the bell is “probably genuine”.
“The bell has never been reported found, but given the extent to which the site was stripped of non-ferrous metals in the past I’d be very surprised if the bell was still on the wreck,” Gribble told the BBC. “The bell looks right. It’s the right sort of size for a bell of that period.”
The BBC reported that Britain’s Receiver of Wreck said the bell “would probably be given to a museum while a decision was made about its future”, adding that the South African government had been notified of the find.
The SS Mendi went down on February 21, 1917, claiming the lives of 607 volunteers of the South African Native Labour Contingent, and nine of their white officers, after being struck in thick mist by a larger vessel, SS Darro, sailing at speed.
The Mendi tragedy was South Africa’s second-biggest loss in the war after the attrition of Delville Wood some months earlier, in 1916.
The Mendi troops, most of whom drowned, were men of the 5th battalion of the South African Native Labour Contingent, all of them volunteers. Among the dead were three Pondoland chiefs, Henry Bokleni, Dokoda Richard Ndamase and Mxonywa Bangani.
The troops were bound for the French port of Le Havre, where they were to have joined the ranks of a mammoth labour corps drawn from elsewhere in Africa, the Middle East, Asia and the Caribbean.
In the century since, the Mendi disaster has become a symbol of unrewarded black valour and the depredations of 20th century history.
Though Prime Minister Louis Botha and the entire House of Assembly rose in silent respect when news of the catastrophe reached South Africa in March 1917, the tragedy of the Mendi, then and in the intervening century, was deepened by the politics of racial discrimination that governed the treatment of the black wartime volunteers, and their neglect when the war ended.
Unlike every single labour corps veteran from other countries - including Swaziland, Botswana and Lesotho, and all the other states across the world - not a single black South African received the British War Medal.
And for those who believed that volunteering to serve in Europe in defence of king and country would be rewarded politically at the cessation of hostilities, all they got was more deprivation and harsher discrimination.
An enduring feature of the Mendi mythology is the account of chaplain Isaac Wauchope Dyobha rallying the doomed men on the deck of the Mendi, leading them in a “death drill”.
There are no survivors’ accounts of this, but for much of the past century it has been central to the Mendi catastrophe narrative.
The Mendi deaths are memorialised at various sites in South Africa, Britain and Europe. In 2003, the Mendi Medal was introduced as South Africa’s highest honour for bravery.
The tragedy is remembered in the naming of two South African Navy vessels - the Valour class frigate, SAS Mendi, which laid a wreath in 2004 where its namesake went down, and the missile boat SAS Isaac Dyobha.
In 2009, Britain’s Ministry of Defence designated the wreck as a protected war grave, making it an offence to remove items.
The wreck site and the Hollybush Cemetery in Southampton - where some of the Mendi dead are buried - were the focus of commemorative events on the centenary of the disaster in February.