“Those speeds took a lot of heat. A lot of explosions going on in that engine.” She directed this at Thor.

“If I can’t see it, it doesn’t count,” said Alf.

“I think I can draw enough ambient heat. Without the load of fuel, it’ll be much more maneuverable.”

Buck heard it, but was she insane? Without fuel, an airplane could take off more easily, too—except for that little thing about not being able to work up enough speed.

“About how much gasoline is left?” asked Gerd.

“Oh, at the speed we were going, we used up half a tank.”

“Well, use up the rest,” said Gerd. “I don’t want to run the risk of the gas tank exploding when I get to work.”

Buck took in a breath, about to challenge this insanity, but the four-star clicked his tongue. “Let’s just watch and see,” he said to Buck.

Alf did not go back to the tank; neither did anyone else. But it started moving again, as fast as before, and in a wide circle. Alf didn’t even look at it. Instead, he came up to the four-star. “All of the design flaws I pointed out to you will need to be corrected.”

The four-star raised an eyebrow. “Looks and sounds like she’s running beautifully.”

“I made some alterations of my own,” said Alf. “It’s better if it comes off the assembly line with a good design instead of having to jerry-rig it afterward.”

Jerry-rig? By caressing the armor plating? But the four-star seemed to think this was all rational, and Buck held his tongue. Besides, it was obvious that something had controlled the tank, and it wasn’t the crew. It made no sense, but Alf was in command of the tank as surely as if it was Bucephalus and he was Alexander.

It wasn’t long before the tank’s engine fell silent and it coasted to a very quick stop. “Empty enough for you?” asked Alf.

“You tell me,” said Gerd. “I don’t work with internal combustion.”

“Till now,” said Thor.

She didn’t even look at him. Instead she closed her eyes for a long moment.

Then the engine came back to life.

“Oh, no, dearie,” said Alf. “It can’t run on hydrogen.”

“And yet it is.”

“Well, yes, but it’s not the fuel it was designed for.”

“Water vapor is everywhere,” said Gerd. “I just separate it electrically and we have all the hydrogen we need. Then it burns and comes out as steam. I think it’s elegant.”

“There’s a lot less water vapor in the desert,” said Thor helpfully.

This time Gerd glared at him. “Those desert savages won’t matter if tanks no longer run on petroleum.”

“Hydrogen will require a complete redesign of the engine, dear,” said Alf, “and we need quick results.”