BUNDABERG's Christopher McRae will play the lead role in a war documentary to be aired on the History Channel internationally, .

Known Unto God , directed by John Schindler, sees 22-year-old McRae play the role of Coogee surf lifesaver turned Z Special unit soldier John Hayes Whitworth, known as Spike, in the 52-minute documentary.

Spike, unknown to all but his immediate military comrades, was a member of the Z Special Unit - the highly secretive forerunners to the Special Air Service (SAS).

Schindler said the elite group conducted dangerous missions in the Pacific deep in enemy territory in the Second World War.

The documentary uncovers the truth about the highly secretive operation and the tragic outcome for Spike whose heroic deeds remained "known unto God" for more than 60 years.

Despite little acting training, Christopher was recruited to the role when Schindler called his father, Michael McRae, a former work colleague and asked if he knew anyone who fit the bill.

"I said to him, I'm looking for a young man, a 20-year-old who looks like the man in our documentary to play the part," Mr Schindler said.

Spike, as he was known by his Coogee Surf Life Saving Club mates, was a 20-year-old tall, bronzed Australian surf lifesaver, the typical Australian male of the 1940s.

"Michael said to me 'Well how about my son Christopher? He's 20 now'," Schindler said.

Schindler said when he found out McRae looked just like Spike and was also a surf lifesaver he knew they'd found their lead.

"That's very important to us. We're documentary makers," Schindler told the NewsMail.

"It all worked perfectly."

Schindler said putting the documentary together was a "labour of love" and said McRae was a delight to work with, even while wearing the replica army attire in 40-degree heat while filming in Toogoom.

"He never complained," he said.

"He was very co-operative, a quiet, nice bloke.

"He did a good job.

"We had technical experts as well showing the boys how to walk as soldiers."

The documentary, which pays tribute to the unsung heroes of the highly secretive Z Special unit, and to fallen Australian surf lifesavers lost in all wars, will be aired on the History Channel on Foxtel.