Button is actually a briefcase

He boasted about the size of his button, but launching a nuclear strike from the US involves a ‘‘football’’ and a ‘‘biscuit’’ - not a switch on President Donald Trump’s desk.

The idea of a button creates a dramatic impression of instant Armageddon but is fantasy. Even so, the time taken from detection of an incoming missile attack to nuclear retaliation is only a matter of minutes, perhaps five at most.

In the US, the ‘‘football’’ is the name given to the bag containing nuclear instructions which is held by a military assistant. He is never more than a few feet from the president.

The ‘‘biscuit’’ is a laminated card, similar in shape and size to a credit card, which the president carries at all times.

In times of nuclear crisis he will call an emergency meeting in the Situation Room, a small, windowless area underneath the White House.

The president will seek consensus from the secretary of defence for a launch, then a senior military officer reads out a ‘‘challenge code’’ - normally two phonetic letters, such as Romeo Delta.

It is a challenge to the president to prove who he is. The president then removes his ‘‘biscuit’’ card and reads out his two letters which authenticate the initial launch process.

With less than two minutes gone, the Pentagon sends a coded signal to missile crews. This is short, about 25 words, containing the missile launch codes and attack plan. - The Times