In May 1962, Soviet Red Army officer Vadut Khakimov received urgent orders calling him back from leave to rejoin his secret military unit in the southwestern Russian region of Bryansk.

His unit, specialised in inspecting nuclear warheads before they were installed on missiles, was given cryptic commands to prepare for "manoeuvres in the north of the country".

Along with tens of thousands of other Soviet troops, Khakimov set off on a cargo ship. The men were dressed in civilian clothes and carried with them ski goggles, fur-lined winter boots -- and no identity papers.

Their operation -- a mystery to all of them -- was called Anadyr, after the Soviet Union's most northeasterly city that lies just 500 kilometres (300 miles) from the eastern maritime border of the United States.

But Khakimov was headed nowhere he would need ski goggles. The winter equipment was just one part of an elaborately concealed security operation.

He was going to Cuba.

Khakimov was about to play his role in the Cold War showdown that saw the Soviet and US superpowers teeter on the brink of nuclear conflict, the October 1962 Cuban missile crisis -- known in Russian as the Karibski krizis (Caribbean crisis).

In an interview with AFP, Khakimov recalled the men had waited 11 hours in July 1962 for their cargo ship the Izhevsk -- loaded with the sophisticated nuclear inspection equipment -- in the Baltic port of Baltiisk in the Soviet Union's Kaliningrad region.

"It was only 30 years later that I understood that it was in those hours that our secret services stuffed the cargo with explosives which their agents could detonate in the case of an American attack," he said, referring to munitions the Russians would have detonated to protect valuable equipment falling into American hands.

--- 'Three envelopes' ---

His unit's sophisticated equipment for checking the nuclear warheads was hidden on the boat's bridge under a metal cover and a load of agricultural material, in a bid to evade infrared detection by American spy planes.

The warheads themselves were carried on separate ships and would arrive on Cuba later.

Khakimov recalled how the Soviet authorities had taken every possible measure to ensure the operation was clouded by the utmost security.

"Even the captain of vessel did not know our true destination.

"He had to open three envelopes successively. The first was opened after leaving Soviet waters and the last one in the Atlantic Ocean. Only then did he know his task was to head for Cuba."

According to Khakimov's information, Soviet leader Nikita Khrushchev between July and October 1962 sent 80 cargo ships to Cuba as a response to US efforts to topple Cuba's Communist regime.

Just two carried the nuclear warheads themselves and the rest missiles, lorries, aircraft and also three military hospitals.

"The voyage took 17 and a half days and I will never forget it," Khakimov recalled. "American planes were following our ship and we could only briefly go up to the bridge at night."

The conditions on board were horrendous. Some 300 soldiers were squeezed into the ship's hull, where temperatures could reach up to 50 degrees Celsius (122 Fahrenheit). Seasickness was legion and the food dire.

On August 3, Khakimov's 29th birthday, the Izhevsk sailed into the Cuban port of Mariel, where the precious cargo was unloaded under the cover of darkness.

"Only the officers were allowed to work on taking the cargo off the ship," he remembered.

With the Soviet authorities keeping up their efforts to disguise the operation to the maximum, the soldiers were given checked shirts so they could pass for Cuban agricultural workers.

They then travelled south by railway to the palm trees of Santiago de Cuba. The first nuclear warheads arrived on another ship at the end of September.

"We installed a total of 40 nuclear warheads on FKR-1 missiles," Khakimov said.

--- 'We helped prevent WWIII' ---

The American jets kept up their reconnaissance missions over Cuba but Khakimov believes they were not effective due to poor weather.

"On October 27, we were told that an American U-2 had been shot down. We thought then that a war was imminent. We would all have to die," he said.

But then with the danger of apocalypse apparently real, the governments of President John F. Kennedy and Khrushchev managed to agree a compromise to avert war.

"One fine day at the end of October the commanders told us, 'Your mission is accomplished and the Americans are not going to touch Cuba'."

His unit left Cuba at the end of December, this time without making too much effort to disguise themselves or their cargo.

Fifty years on, Khakimov is the head of an association of Soviet veterans of the missile crisis.

He said the Kremlin should award the status of "frontline veteran" to the 2,500 participants in the Anadyr operation who are still alive. This would add a modest 1,000 roubles ($32, 25 euros) to their monthly pension.

"Even if there was no fighting, we helped ensure that there was no World War III," he said.