Blooper

It is highly improbable that any systems (even nuclear launch systems) could be still powered after a full year with out someone alive to maintain them. If all human operators would vanish from a nuclear power plant it is safe to assume that something bad would happen very soon.

The ARS (a device that launches many nuclear missiles in retaliation to a strike) is activated by one man pushing a few buttons. Devices that launch nuclear missiles are normally (and believably) portrayed as requiring launch codes, special keys and the authorization of at least two people.

In one scene, Senator Barkley and President Richardson are both quite conscious before they suddenly die of the virus. In reality, a person is usually pretty critical (in a 'grave' state) before they succumb to it.

The backpack radio shown could not transmit up an elevator shaft and then far enough downstream to reach a submerged sub.

Yoshizumi was not far enough underground (of the White House) to survive an atomic missile hit.

Upon entering the bunker, Yoshizumi watches in horror on several monitors as nuclear rockets launch all over the world. The footage on many of these monitors feature hand-held camera work. Due to the virus sweeping the world many months earlier, there would be no one alive at that point to be operating these cameras.

The chamber where the ARS is located is reached by Yoshizumi and Carter simply blowing two doors open with plastique and climbing down an elevator shaft. A chamber containing a doomsday device probably contains more elaborate security features, such as blast doors.

Major Carter points out to Admiral Conway that selecting a random person (by them unfolding a particular playing card) to head to Washington D.C. and deactivate the nukes is 'stupid', then Carter states that he himself is the most capable to do the mission. Later, Yoshizumi tries to join Carter by showing him that he unfolded the particular card and has to join him, that would be useless since the idea (by choosing a random person) was withdrawn before it could get started.

After it's described on the on-screen text that most (or almost all) people (esp. those living in major cities) in both the U.S. and Europe have died from the virus. President Richardson, General Garland and Senator Barkley appear to be lucky people being among the last ones to die of it.