Advance, as the under-water ship was called, was begun.

It was soon to be launched in a large creek that extended
in from the ocean and had plenty of water at high tide. Tom
and Mr. Sharp made several trips back and forth from Shopton
in their airship, to see that all was safe at home and
occasionally to get needed tools and supplies from the
shops, for not all the apparatus could be moved from Shopton
to the coast.

It was when returning from one of these trips that Tom
brought with him the paper containing an account of the
wreck of the Boldero and the sinking of the treasure she
carried.

Until late that night the three fortune-hunters discussed
various matters.

"We'll hurry work on the ship," said Mr. Swift it length.
"Tom, I wonder if your friend, Mr. Damon, would care to try
how it seems under Water? He stood the air trip fairly
well."

"I'll write and ask him," answered the lad. "I'm sure
he'll go."

Securing, a few days later, the assistance of two
mechanics, whom he knew he could trust, for as yet the
construction of the Advance was a secret, Mr. Swift prepared
to rush work on the submarine, and for the next three weeks