Trump wasn't at the inauguration to hand Biden the nuclear 'football.' The transfer happened differently for the very first time.

Traditionally the nuclear "football" — the heavy briefcase that's always with the president, who can use it to control America's nuclear weapons — is handed off by the outgoing commander in chief to the incoming president at the inauguration, NBC News reported.

But not this time.

What are the details?

A military aide who carries the "football" remains physically close to the president, the network said, and is ready at a moment's notice to commence the detailed process of putting the football to use.

But former President Donald Trump wasn't on hand to witness President Joe Biden take his oath of office Wednesday, so instead of Trump doing the handoff, it's happening in a different way for the very first time, the network said.

More from NBC News:

A U.S. official said that a military aide will accompany Trump to Florida with one of the footballs and that Trump will retain sole authority to launch a nuclear strike until 11:59:59 a.m. Wednesday. Trump's being physically out of Washington will not affect his launch authority or access to the football until noon. (There are multiple footballs that allow a president to launch a military strike while traveling.)

Another military aide with a second nuclear football will hand over the authority to Biden once he is sworn in, the official said, and the military aide with Trump will bring the football back to Washington.

Retired Navy Adm. James Stavridis, also an NBC News contributor, said the football with Biden becomes — at noon — the one that's "activated" and that U.S. Strategic Command will go to that football, the network reported.

"Right before he becomes president, there's a football in his vicinity [that] is activated," Stavridis told NBC News of Biden.

The network said the White House declined to comment on the matter due to security.

Anything else?

Former Vice President Dick Cheney described in a 2013 Discovery Channel documentary how it all takes place, NBC News noted:

"The passing of the football occurs at high noon. Nobody says a word, but I knew what to look for," he said. "So you've got the ceremony going down front, but ... sort of behind one of the big pillars there in the front, these two guys are standing there in their uniform, and at the right moment he reaches over to hand it to the newly designated military aide. And he takes it from that moment on. The new president is the guy who's in control of our nuclear assets."

Michael Beschloss, a presidential historian and NBC News contributor, told the network some unusual events involving the nuclear football have occurred under various presidents.

Beschloss said the football's location "was an issue" when former President John F. Kennedy was assassinated in Dallas in 1963 and that "[former President Ronald] Reagan's nuclear code card was accidentally thrown out at the hospital after he was shot in 1981. [Former President Bill] Clinton lost his nuclear code card for a few months in 2000."