"Ach! You may walk at my side," permitted the German.

It all seemed a bit strange, but Captain Jack Benson had been through
more strange experiences than had most Americans of twice or thrice his
age. Besides, as he walked beside Herr Professor Radberg Jack imagined
that he had guessed at least an inkling of the other's business. The
German had announced himself as a professor; probably, therefore, he was
a scientist. Being a scientist, the Professor had very likely invented,
or nearly invented something intended for use in connection with
submarine torpedo boats, and wanted to interest the concern by which the
young submarine skipper was employed. Though this guess was a
reasonable one, it soon turned out to be the wrong one. The Professor's
real reason for seeking this interview was one that was bound to take
the submarine boy almost off his feet.

Readers of the preceding volumes in this series need no introduction to
Captain Jack Benson, nor to his chums, Hal Hastings and Eph Somers.
Such readers recall, as told in "_The Submarine Boys on Duty_," how
Jack and Hal drifted into Dunhaven just at the right moment to fight for
an opportunity to work themselves into the submarine boat building
business. How the boys helped build the first of the now famous Pollard
submarines, and afterwards learned how to man her, was all told, together
with all their strange adventures in their new life.

In the "_The Submarine Boys' Trial Trip_" was related how Jack Benson
solved the problem of leaving a submarine boat when it lay on the
ocean's bottom, and also the trick of entering that submerged boat
again, after diving from the surface of the water. The attempt of
shrewd business men to secure control of the new submarine boat company
was also described, together with the manner in which the submarine