WMG / The Final Countdown

The Soviet spy ship is following the Nimitz because of what happens to it.

The Russians have evidence that something the Americans did, likely involving the USS Nimitz, somehow seems to have played a part in the events of WWII and their aftermath. It's considered crazy by almost everyone, but the accumulated evidence is substantial and provocative. Being routinely surveilled as a major business head with strong DOD ties, they are aware that Richard Tideman has had an astonishing history of success, with very little failure.

Most astonishing of all is that Richard Tideman and commander Richard Owens of the Nimitz are shockingly similar people AND HAVE THE SAME FINGERPRINTS. They are further aware that Tideman has played a hidden supportive role in Owen's life, and that Tideman was heavily involved in this particular mission of the Nimitz. He has pulled strings to ensure the Nimitz departs on this specific mission lacking almost its entire escort fleet.

Despite the awesomeness of of the armada of modern aircraft moving to intercept the Japanese fleet, they would have been destroyed or failed for some reason to preserve the time stream.

Two people left behind is one small thing - a huge event like preventing Pearl Harbor would have been catastrophic. Maybe a Japanese submarine would have sunk the Nimitz with an incredibly lucky shot. Maybe a freak up/downdraft would have sent all the planes into the ocean.

The storm returned because they were about to commit a huge change on the time line.

The Nimitz inadvertently invoked the circumstances for them to return home.

The Nimitz was Doc Brown's prototype

He decided that a DeLorean would be a better idea.