'Moving fortress': Kim Jong Un's bulletproof train

An olive green North Korean train, emblazoned with a gold stripe, trundled across the border into Russia Tuesday, carrying North Korea's Kim Jong Un to a meeting with President Vladimir Putin.

Since taking power in 2011, Kim has made seven international trips, and crossed the border into South Korea twice, using his special train for the majority of his overseas travel.

AFP takes a look at what we know about Kim's preferred modes of transport:

From his 2018 trip to Beijing to a 60-hour journey to Hanoi for a summit with then-US president Donald Trump, Kim has used his train for many high-profile trips.

A love of locomotives runs in the family: Kim's father Kim Jong Il was known for his fear of flying, limiting his foreign trips to overland journeys to China and Russia by armoured train.

The elder Kim once took his train from Pyongyang to Moscow in 2001, a marathon 20,000-kilometre (12,400-mile) round trip that took about 24 days.

The train was well stocked, however, with fresh lobster and cases of French Bordeaux and Burgundy red wines, according to an account by Russian official Konstantin Pulikovsky, who was also aboard.

According to the official North Korean account, Kim Jong Il was on a train for a "field guidance" visit in 2011 when he died of a heart attack.

The carriages used by Kim Jong Il and by his own father and predecessor, the North's founder Kim Il Sung, are now on display at the Kumsusan Memorial Palace in Pyongyang, where both late leaders' bodies lie in state.

The Kims reportedly have several almost identical special trains made by a factory in Pyongyang.

Nicknamed the "moving fortress", Kim's current train has bulletproof windows and reinforced walls and floors to protect against explosives, according to Seoul's unification ministry.

"It is equipped with attack weapons and a helicopter for escape in case of emergency," the ministry says, adding that due to the weight of all the extra equipment the vehicle moves at only around 60 kilometres (37 miles) per hour.

Despite its slowness, the train has key advantages over an aircraft, it said, chiefly offering more flexibility in unforeseen circumstances, including attacks.

Were an aircraft with Kim on it to be attacked, "survival chances are significantly reduced", it said.

The ministry said it was also "more challenging to predict train itineraries".

To bolster on-board security measures, Pyongyang has in the past asked for guards to be deployed along the tracks, as it did for Kim's 2019 Hanoi visit.

Kim has made seven previous overseas trips -- four to China and one each to Russia, Vietnam and Singapore. The latter two were for summits with Trump.

He has also crossed the border into South Korea twice.

Unlike his father, he is not scared to fly: he flew on three trips -- two to China, and one to Singapore -- and has even been shown at the controls of an aircraft in 2014 state media footage.

His private plane, which flew him to China in 2018, is known as "Chammae-1" after the national bird of North Korea, and is a Cold War-era Russian-made Ilyushin-62.

Analysts question the aircraft's reliability due to its age and possible maintenance issues.

The "Chammae-1" flew to Singapore in 2018 when Kim was heading to the city to meet Trump -- but the North Korean leader was not on board.

Instead, he flew on an Air China 747 provided by Beijing, Pyongyang's most important ally.

According to flight tracking website Flightradar24, the plane took off using flight number CA122, a standard designation for the airline's route from Pyongyang to Beijing. In mid-air, it changed its call sign to CA061 and headed south.

At the time, analysts suggested China had lent a jet to Kim as a way to assuage his safety concerns, in a bid by Beijing to ensure it was not sidelined at a summit where Washington-Pyongyang ties looked set to improve.

But Kim and Trump's rare bout of diplomacy collapsed in 2019 anyway.

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