Dr Denny Roy grew up during the Cold War seeing "fallout shelter" signs on certain buildings, viewing cartoonish TV public service messages on how to react to air raid sirens, and participating in "disaster drills" at school.

But that ended a long time ago. So early last Saturday morning in bucolic Honolulu, when Dr Roy was watching a basketball game on television and saw the warning, "Ballistic missile threat inbound to Hawaii. Seek immediate shelter. This is not a drill", he felt, for the first time, the "physical sensation of terror".

But Dr Roy is a political science professor and senior fellow at the East West Centre. In about 60 seconds, his intellect took over.

Targeting Hawaii would mean instant retaliation and the end of North Korean leader Kim Jong Un and his regime, he told himself. Why would Mr Kim do this when North and South Korea had just held talks?

But with North Korea flaunting its missile capability and President Donald Trump seeking more nuclear weapons for the United States, the episode was a throwback to the Cold War days.

"Now some of us in Hawaii have experienced what you could call the return of nuclear war anxiety," Dr Roy told The Straits Times.

America's 2018 Nuclear Posture Review is due next month but the Huffington Post reported last week that the document seeks more low-yield nuclear weapons as "supplements" that will "enhance deterrence".

This has raised concerns among security analysts. "The Trump Nuclear Posture Review (NPR) is about as bad as expected. Calls for new, 'more usable' nuclear weapons and expands the number of scenarios that might lead Trump to use nukes," Arms Control Association director Daryl Kimball said in a tweet.

In an e-mail to The Straits Times, Mr Kimball wrote: "The false missile attack alarm in Hawaii is one of many signs that we are entering a new and more dangerous nuclear era."

"Nuclear accidents and mistakes... can (happen) and will lead to miscalculation, which can lead to catastrophe if we or our nuclear adversaries launch a real attack in response to a false alarm or a poorly phrased presidential tweet," he warned.

"Rather than actively seeking to engage other nuclear actors to reduce these risks through smart diplomacy, the Trump administration is adopting a nuclear strategy that expands rather than narrows the circumstances in which the United States might use nuclear weapons," he added.

This comes amid discussions on whether there should be some checks and balances on President Trump's power to order a nuclear strike.

Mr Will Saetren, a research associate at the Institute for China-America Studies in Washington, told The Straits Times: "Taken alone, this (false alarm in Hawaii) wasn't that big a deal. But given this President, and the strategic environment he has created, it could lead to misinterpreted signalling that could spark a war that nobody really wants."

"The real fear is that North Korea could see this as a legitimate attempt by the Americans to use this as a pretext to launch a pre-emptive strike on North Korea."

On the NPR, he said: "The US can meet all of its deterrence requirements with a reduced arsenal. We have to invest in command and control and updating what we have decided to keep. But... giving ourselves options and fooling ourselves that even low-yield nuclear weapons are somehow usable, is doing ourselves a really big disservice."

The last five words of Saturday's false alarm have a special resonance in Honolulu, where a gleaming white monument to those who died in Japan's devastating Dec 7, 1941 surprise attack marks the azure waters of Pearl Harbour.

"Air raid Pearl Harbor. This is not a drill" was the frantic radio message that went out that day as American warships burned and sank under the onslaught.

More than 75 years on, the spectre of an equally terrible war involving the US has risen again.