Today he finds himself on the front line of a very different sort of war. He lives in the jungles of the war-torn Democratic Republic of Congo, battling to stop poachers killing the last few northern white rhino left on the planet.

Lieutenant-Colonel Thorpe, 41, who left the Royal Marines last year after more than a decade in the Special Boat Service, could now be earning at least £1,500 a day on the burgeoning private security circuit in Afghanistan or Iraq.

Instead he has returned to the continent of his birth to train ageing, malnourished and battle-weary Congolese Rangers to take on well-armed poachers crossing the border from neighbouring Sudan. Scores of rangers have been killed defending their country’s wildlife in recent years, but these ones have permission to shoot-to-kill.

“The mission is urgent,” said Lieutenant-Colonel Thorpe at his base in an abandoned tourist resort on the Semliki river, a four-hour flight from the capital, Kinshasa. “If the Congo is to recover, it will be through its use of natural resources and that includes tourism. But the gorillas are in danger, elephants have been almost entirely poached out, and now there are just a handful of white rhino left.”

Congo used to have abundant wildlife, but poachers ran amok during the five years of war that ended in a fragile ceasefire in 2003. The elephant population has been almost wiped out. So has 80 per cent of the country’s hippopotamuses.

Lieutenant-Colonel Thorpe’s mission has been approved by the Congolese Government, and is funded by the EU, USAid and the Frankfurt Zoological Society.

His first priority was to help to secure the tiny remaining population of gorillas, known as lowland gorillas of the mountains. But his task now is to save the last of the northern white rhinos, which are slaughtered by poachers for their horns. Only five of the docile, short-sighted creatures are known to survive, all living in what was the Garamba National Park. About 600 park rangers, wearing flipflops and tattered uniforms, volunteered to join Lieutenant-Colonel Thorpe. After months of gruelling endurance and battle drills more familiar to commandos than conservationists, they were reduced to a unit of 33.

During his career in the SBS, Lieutenant-Colonel Thorpe had state-of-the art weaponry. In the Congo — assisted by his brother Seamus, Mike Roberts, who served with 1st Parachute Regiment for four years, and Paul Naish, a veteran of South African military intelligence — he had to cobble together weapons together from broken AK47s, and supply his men with protein in the form of fish confiscated from poachers.

He also has to keep his men away from the Congolese Army. “The army’s been a real problem, we’ve just tried to stay out of their way,” he said.

But the rangers’ morale is higher than it has been in years. “We’ve been well fed, we’ve been well trained, and we’re ready to shoot the poachers before they shoot us,” said Eli Mudima, one of the recruits. “We’re only worried about what happens when Conrad goes — will our funding just get stolen by our bosses? I don’t know. But we’re ready, and at least Conrad came here to show that the Congo’s not been forgotten.”

Lieutenant-Colonel Thorpe scoffs at suggestions that he is helping to create another militia in a country still over run with them. “This isn’t a private army. This is a mission to give morale back to the rangers who’ve been serving the parks loyally for decades, often without pay, and at incredible risk to themselves,” he said.

“It’s been a shock to be away from an organised army. But this will make a difference. Someone has to stand tall in the Congo and say, ‘The law starts here, with me’. That’s what we’re doing.

“I’m here because I want to put something back. I was born in Africa and wanted to start my retirement from the Royal Marines by doing something a bit different. And boy-oh-boy did I get my wish.”

HORN OF AFRICA

Sam Kiley’s film, Guns for Hire — Congo, is on Sky One on Monday at 10pm.

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