looked over the ship before turning in for the night. The
craft was made immensely strong to withstand powerful
pressure at the bottom of the ocean. The submarine could
penetrate to a depth of about three miles. Below that it was
dangerous to go, as the awful force would crush the plates,
powerful as they were.

"Well, we'll rush things to-morrow and the next day,"
observed Tom as he prepared to leave the building. "Then
we'll soon see if it works."

For the next week there were busy times in the shop near
the ocean. Great secrecy was maintained, and though
curiosity seekers did stroll along now and then, they
received little satisfaction. At first Mr. Swift thought
that the visit of Mr. Berg would have unpleasant results,
for he feared that the agent would talk about the craft, of
which he had so unexpectedly gotten a sight. But nothing
seemed to follow from his chance inspection, and it was
forgotten.

It was one evening, about a week later, that Tom was alone
in the shop. The two mechanics that had been hired to help
out in the rush had been let go, and the ship needed but a
few adjustments to make it ready for the sea.

"I think I'll just take another look at the water tank
valves," said Tom to himself as he prepared to enter the big
compartments which received the water ballast. "I want to be
sure they work properly and quickly. We've got to depend on