When they returned to the surface the metal cylinder was in place below.
Glancing backward only once, to make sure that Williamson was not yet on deck, and that the gunboat's marine guard had not detected their stealthy work, the swimming pair struck out lustily for shore.
Back into the same clump of bushes they made their way. In the first few moments neither of the recent swimmers appeared to dare a glance into the face of his comrade. In silence they fitted the shore end of the wire to the battery.
Then one of the pair seized the handle to pomp the fatal electric spark along the wire to the hidden mine under the "Benson's" hull.
"Remember what happened to the 'Maine'!" this wretch chuckled hideously.
CHAPTER XIX
A JOKE ON THE SECRET SERVICE!
"What's that noise?" wondered Williamson.
He stopped, listening intently, for he was still below.
Against the bottom of the "Benson's" hull he heard a steady, slow, monotonous bumping. As he listened, his face took on an anxious look.