get set for an ultimatum to the United States to backwater or be
bombarded from space."

Mike said crisply: "How long before they can do it?"

Major Holt turned uncordial eyes upon him. "It's anybody's guess. Why?"

"We've been working something out," said Mike, firmly but in part
untruthfully. He stood sturdily before the major's desk, which he barely
topped. "The four of us have been working it out. Joe says they've done
powder metallurgy welds, back at his father's plant. Joe and Haney and
the Chief and me, we've been working out an idea."

Major Holt waited. His hands moved nervously on his desk. Joe looked at
Mike. Haney and the Chief regarded him warily. The Chief cocked his head
on one side.

"It'll take a minute to get it across," said Mike. "You have to think of
concrete first. When you want to make a cubic yard of concrete, you take
a cubic yard of gravel. Then you add some sand--just enough to fill in
the cracks between the gravel. Then you put in some cement. It goes in
the cracks between the grains of sand. A little bit of cement makes a
lot of concrete. See?"

Major Holt frowned. But he knew these four. "I see, but I don't
understand."

"You can weld metals together with powder-metallurgy powder at less than
red heat. You can take steel filings for sand and steel turnings for
gravel and powdered steel for cement--"