HALIFAX -- It's an apology more than a century in the making.

The men of the No. 2 Construction Battalion were treated like second-class citizens during the war, but their contributions were invaluable.

It was the only all-Black battalion to serve in the First World War and its members found themselves segregated from others.

Based in Pictou, N.S., they weren't considered good enough to carry rifles, so they were handed shovels, saws and axes instead.

Along with roads and bridges, they cut the timber that lined the trenches for Allied troops.

"The work that they did under pretty difficult circumstances was invaluable to the war-effort," says Ken Hynes, curator of The Army Museum at Halifax Citadel.

Now, almost 105 years after the group formed, Ottawa is determined to right past wrongs by offering an apology for the way the men were treated.

CTV News has learned it will come this Sunday.

"Actually, if it weren't for the work they were doing, there might have been a different outcome in the war," said former NDP MP Gordon Early.

Although the initiative began decades ago, Earle put it on the prime minister's radar with a letter two year ago.

"Here you had young men, willing to serve their country, willing to fight for their country, and die for the country if necessary, and yet they were being told that they couldn't do that," Earle said.

Others say it's long overdue, too.

For lawyer Douglas Ruck, the battalion has always been a family matter:  his father literally wrote the book on the topic in 1987.

"The families of those men -- and African-Canadians in general -- deserve the apology," Ruck says. "It needs to be heard and it needs to be given with commitment and sincerity."

Hynes agrees.

"I think it's a laudable thing to do," he said. "It's an important thing to do, and I think it's long overdue."

There is a modern consensus on a loyal battalion that is now celebrated, after a betrayal when they signed up to serve.

Like almost everything else these days, Sunday's event will be a virtual one, but well represented. Beyond the defence minister, and veterans affairs, even the prime minister's office will participate.