And what exactly is the point of having a machine gun in a power plant???

More from the same NYT article:

Inside the reactor building, near the entrance to the primary containment structure, are carefully marked spaces with two lime green carts about the size of hand trucks that a supermarket worker might use to roll cases of soda cans to the proper aisle. Each is loaded with batteries.

One cart could power the instruments that measure the water level in the reactor vessel, an ability that Japanese operators lost a few hours after the tsunami hit. Another could operate critical valves that failed early at Fukushima.
....

Deeper into the building, in an odd-shaped space in the basement between a corner of the square reactor building and the round containment shell is a steam-driven pump. This is something that the designer, General Electric, intended to be available to deliver up to 600 gallons per minute of cooling water into the reactor core even if the electrically driven pumps failed for want of power. An overheating reactor would be likely to have ample supplies of steam to run it.

That worked at Fukushima for a while but appears to have stopped functioning later; the Japanese plant's operator, the Tokyo Electric Power Company, has not provided an explanation. Again, the T.V.A. suggests that it has backup tools that the Japanese utility, known as Tepco, probably lacked: a battery-powered strobe light stored in a nearby cabinet, and a valve that usually runs on electricity but also has a hand crank.

They obviously have backup for the bullshit.

The only significant item, really, is the steam driven pump, which Fukushima also had. It possibly failed at Fukushima or would fail elsewhere because of loss of pressurization inside the reactor, possibly due to thermal failure of gaskets. Now if they had on site natural gas powered electrical generators capable of powering the heat exchanger pumps and hardened CNG storage adequate for a month's operation, I would say they had some significant backup to their diesel backup generators.

It is nice to be able to see just how high the temperatures and pressures are getting via battery power. It would be much better to be certain of being able to do something about it. But that might cost more money.

"It is not necessary to have hope in order to persevere."

why do you have electrical cables and air hoses (?) draped haphazardly from the ceiling???

Maintenance operations during a planned shut down? But what would they do during an emergency shutdown when they might want the entryway through which they are passing to be sealed?

"It is not necessary to have hope in order to persevere."