THERE’S no doubt the rhetoric coming out of North Korea is alarming.

Pyongyang has said the approaching American armada is a “grim action” that could bring “catastrophic consequences” to the world.

Indeed, if history is any guide, there’s one time of the year America needs to be worried about North Korea turning its anger into action — and it’s right now.

April 15 is the anniversary of the birth of Kim Il-sung, the dictator who founded the nation and is the late grandfather of current leader Kim Jong-un.

It’s a time when the regime is prone to hubris. This hubris which turned deadly in 1969 when, with a single shot from a fighter jet, the North felled a US spy plane killing 31 sailors.

The incident has almost been forgotten but it’s been reported that at the time US President Richard Nixon was so incensed at the act that he came close to ordering a nuclear strike.

North Korea has never apologised for its actions, nor was it ever militarily punished.

An analysis by a former US intelligence officer said the “calm deliberation and precision of the shoot down” suggested the 1969 downing had long been in the planning.

If you think the 2010s are a nadir in US-North Korea relations, try the late 1960s.

The Korean War was still fresh in people’s memories and in January 1968, the American spy ship USS Pueblo had been captured by the North. One US sailor died in the attack and 86 others were held in captivity for almost a year.

Just months after they were freed, on a Tuesday morning in April, a US Lockheed EC-121 propeller driven spy plane, known by its radio call of Deep Sea 129, took off from a base in eastern Japan.

It tracked north-west towards the coast of North Korea.

So long as its route remained above international waters, the US crews hoped they were in the clear.

“Two-hundred of these flights were executed without incident in just the first three months of 1969,” said Captain Dave Wright of the US Navy at a 2013 service in Japan to mark the anniversary of the downing.

But, for some time, Pyongyang had not been in a tolerant mood.

Richard Mobley, a former US naval intelligence officer, wrote an analysis of the EC-121 shoot down for the CIA’ s Centre for the Study of Intelligence in 2003.

“The North Koreans had long been sensitive to ships and aircraft operating off their coasts,” he wrote. US planes had already been damaged and South Korean boats sunk. It should have been no surprise they might look for another scalp.

As Tuesday progressed, the EC-121 aircraft neared North Korea and began to circle some 120kms off the coast to see what information it could gather.

At about 12.30pm, several Russian built MiG jets took off from a North Korean base and headed towards the plane.

This did not go unnoticed by US radars in Korea who warned the crew but the aircraft made no acknowledgment of the warning.

At 1pm, Deep Sea 129 checked in with base, yet did not mention the approaching MiGs. It was the last communication from the plane; around 20 minutes later it fell off radar screens.

“If it did receive the warnings, the EC-121 probably would have begun diving for the sea to gain speed and to drop below enemy radar coverage,” wrote Mr Mobley.

“At a minimum, the aircraft would have turned away from the North Korean coast [to] avoid provocative action.”

Far from being an knee-jerk reaction, Mr Mobley said Pyongyang had likely been planning to attack a US spy plane for some time.

The North Koreans had been observing the EC-121 flight paths. They’d seen how slow and lumbering the planes were and, just weeks earlier, had moved their most powerful fighter jets to a base near the coast.

“The staging of MiGs to a base close to the EC-121 track, the calm deliberation, timing, and precision characterising the shoot down; and the lack of subsequent confusion in North Korean command and control suggest prior planning and national oversight,” said Mr Mobley.

“One [MiG] flew a defensive patrol and approached no closer than 65 miles from the EC-121. The second fighter raced to the EC-121, shot it down about 80 miles off the coast, and immediately returned to North Korean airspace. Simplicity itself.”

Pyongyang justified the downing, saying it was due to the “grave provocation of infiltrating deep into the territorial air space of the republic.”

The air force had scored “a brilliant battle success of shooting it down with a single shot at a high altitude,” it continued.

President Nixon was so livid at the brazenness of the North Koreans his finger was poised above the nuclear button.

George Carver, a CIA Vietnam specialist said that “Nixon became incensed and ordered a tactical nuclear strike ... The Joint Chiefs were alerted and asked to recommend targets,” reported the Guardian.

Bruce Charles, a US fighter pilot stationed at the time in South Korea, had a nuclear bomb stashed in his jet ready to drop at a moment’s notice on a specific North Korean air strip.

In 2010, he told the US National Public Radio (NPR) that he was put on high alert following the 15 April attack.

“When I got to see the colonel, it was very simple. He described the shooting down of the EC-121 about a hundred miles at sea. And that he had a message, saying to prepare to strike my target.”

His bomb was 20 times larger than the one that fell on Hiroshima.

But the final order never came. In Washington DC, National Security Adviser Henry Kissinger reportedly persuaded Nixon to sleep on it.

In the days that followed, the US considered nuclear or more limited conventional strikes. However, there was a concern any strike would start a full-scale war.

“The danger of a wide war tends to trump whatever benefit you think might come from punishing your enemy here with a retaliatory strike,” Dan Sneider of Stanford University, told NPR.

Instead, the US soon after resumed its EC-121 flights, but now with beefed up military escorts. No military strikes ever occurred against the North. Some praised Nixon for his restraint and no further spy planes were lost.

“The EC-121’s mission was never completed, the aircraft was never recovered. Thirty sailors and one Marine never saw home base again,” said Captain Wright of the 15 April incident.

On Saturday, North Korea will once again mark Kim Il-sung’s birthday.

benedict.brook@news.com.au