At Yokota Air Base, about an hour’s drive west of Tokyo, U.S. military manpower and machines are working round-the-clock and have been since this time last week when Japan was plunged into crisis by a massive quake.

The base’s roughly 3,000 servicemen and women, already drained by a week-long exercise, shifted gear and switched their mission in the time it took to make a few phone calls.

Defending the base against potential enemies in the region quickly turned into a very real operation to save thousands of lives in Japan’s tsunami-ravaged north east.

Helicopter pilots like Capt. Kevin Weaver, who would ordinarily rescue U.S. troops from combat zones in Afghanistan and Iraq, found themselves flying north in search of civilian survivors of the devastating wave.

Massive military cargo planes, normally based in Alaska and Hawaii, began arriving to airlift Japanese troops and their equipment from other parts of the country closer to the disaster area.

The Marines, from southern bases in Okinawa, are also here collecting equipment and supplies before heading north to crucial forward operating centers.

In a small corner of a cavernous hangar that is normally used to pack parachutes, bus-loads of military personnel and civilians line-up to be registered and processed through to the where their help is needed.

They come at all hours of the day and night, through the open hangar doors, which let in the frigid air. The wintry blast makes it almost impossible for anymore survivors to be found, but finding survivors isn’t the only mission.

The quakes’ many living victims have to be fed, sheltered, warmed and consoled. The rebuilding effort will take years. It’s a mammoth task that lies ahead of the Japanese government and its international friends.

In an exclusive interview with Fox News the Commander of U.S. Forces in Japan Lt. Gen. Burt Field summed it up.

“We’re going to be dealing with this for a long time. So it’s about staying the course and having the endurance to continue to go back every day and every day to help work through the issues.”

But while the military goes about its collective duty with self-assured professionalism, it’s obvious that behind the scenes there is nervousness here -- evident in whispered cell phone calls home and tearful spouses behind the wheels of Japanese cars at intersections.

The source of the disquiet is located about 150 miles north east of the base. A wrecked nuclear power plant continues to send radiation into the air despite the exhaustive and imaginative efforts of the plant’s heroic workers.

On Thursday the State Department announced it would allow dependants of diplomatic staff to evacuate the country and the Department of Defense soon after told soldiers their families could leave if they wanted to.

For some the decision couldn’t come soon enough. Others will likely chose to stay with their loved ones, but all will agonize over the decision. The planes taking families out of the potential red zone and to a designated ‘safe haven’ will start landing from Saturday.

Those left behind will face down the potential dangers and take the appropriate actions and precautions should it become necessary.

Meanwhile, the buses continue to arrive at the hangar doors.

Fox News correspondent David Piper contributed to this report.