"The number of Aboriginal soldiers is always going to be an elusive figure. There are about 1200 [known] but it might be more than that."

The lack of documentation about race in official records makes cross-referencing difficult. But some names and stories have been found, and they have been source material for Black Diggers, which shines a light on a little-known part of Australian military history in the year of the Centenary of Anzac. Only one Indigenous woman – a nurse – has been verified.

"Why did Aboriginals sign up? That's a good question," Wright says.

For some, he says, it might have been entwined in the idea of fighting for land, which their ancestors had started doing in 1788. And unlike some white Australians who might go seeking adventure or who felt loyalty to Britain, for many Indigenous people there tended to be pragmatic reasons. For example, Queenslanders, he says, were in 1914 still under the control of the Aboriginal Protector who confiscated any money earned and doled out a small amount, so the military was enticing.

"Being employed by the federal government they could get access to their full salary."

There was never any racial segregation in the Australian armed forces, he says, and although some Indigenous men faced prejudiced doctors who would not let them in on spurious medical grounds because they looked Aboriginal, others were able to get through and most found there was far less racism in the forces than in Australia. Working together in difficult and dangerous conditions brought men closer.

"When you're knee-deep in mud and blood at Ypres you're not going to worry about the colour of your mates' skin."

But when the Indigenous servicemen were discharged and returned to Australia, the previous attitudes too often prevailed, including in the soldier settlement scheme after the war.

Wright, who is not Indigenous, says he was approached by director Wesley Enoch and researcher David Williams after they had amassed a lot of material from the Australian War Memorial, families, veterans, and historians to create a dramatic work.

"I had about six months, it isn't a long period," he says.

While the director and cast are Indigenous – the latter playing both Aboriginal and non-Aboriginal roles – Wright thinks he was chosen both for his writing experience and to provide a fresh perspective on the project.

Rather than focus on one or two stories or create the sort of narrative used in a film such as Gallipoli – two young country friends go off to war together – it was decided to create a play made up or about 60 quick, short scenes based on the stories of soldiers but with names changed and dramatic licence taken. The cast of nine Indigenous actors play about 100 roles, Indigenous and non-Indigenous, and ranging in time from the 1870s to the 1940s, dealing with the early lives of some men and the later lives of others.

"It's about Australia in the 20th century and how we came to be a society. It's one part of that big story."

Although he's written other plays and opera libretti and worked as an assistant director at the Sydney Theatre Company, Wright says, "I'm not really a playwright in the David Williamson sense."

He works more at adapting existing material – including Shakespeare, into The War of the Roses and Sophocles into On the Misconception of Oedipus – and enjoys working closely with directors and actors to develop it.

"I'm not happy sitting in a room writing by myself."

The story of Gallipoli and the Anzacs seems to be as popular as it's ever been, a century after the historical events, even though all those involved are now dead. Wright says this might be "for want of a bigger national story ... a lot of people are desperate for a national narrative".

And Black Diggers seems to have a place in that narrative, helping to bring unknown stories to the fore. Wright says Black Diggers has been a big hit with the general public.

"Audiences love it, both Indigenous and non-Indigenous."

Black Diggers. Written by Tom Wright. Directed by Wesley Enoch. Canberra Theatre Centre presents a Queensland Theatre Company and Sydney Festival production. March 25-28. Tickets $65-85. Bookings: canberratheatrecentre.com.au or 6275 2700.