The submarine planned by Mr. Swift and Tom jointly, and
constructed by them, with the aid of Mr. Sharp and Mr.
Jackson, was shaped like a Cigar, over one hundred feet long
and twenty feet in diameter at the thickest part. It was
divided into many compartments, all water-tight, so that if
one or even three were flooded the ship would still be
useable.

Buoyancy was provided for by having several tanks for the
introduction of compressed air, and there was an emergency
arrangement so that a collapsible aluminum container could
be distended and filled with a powerful gas. This was to be
used if, by any means, the ship was disabled on the bottom
of the ocean. The container could be expanded and filled,
and would send the Advance to the surface.

Another peculiar feature was that the engine-room, dynamos
and other apparatus were all contained amidships. This gave
stability to the craft, and also enabled the same engine to
operate both shafts and propellers, as well as both the
negative forward electrical plates, and the positive rear
ones.

These plates were a new idea in submarine construction,
and were the outcome of an idea of Mr. Swift, with some
suggestions from his son.

The aged inventor did not want to depend on the usual
screw propellers for his craft, nor did he want to use a jet