contrivance had been adopted. From a great boom
projecting over the stern, a large ship's cannon was
suspended perpendicularly, muzzle downward. This
gun could be swung around to the deck, hoisted into a
horizontal position, loaded with a heavy charge, a
wooden plug keeping the load in position when the gun
hung perpendicularly.

If the crab should come under the stern, this
cannon could be fired directly downward upon her back,
and it was not believed that any vessel of the kind
could stand many such tremendous shocks. It was not
known exactly how ventilation was supplied to the
submarine vessels of the Syndicate, nor how the
occupants were enabled to make the necessary
observations during action. When under way the crabs
sailed somewhat elevated above the water, but when
engaged with an enemy only a small portion of their
covering armour could be seen.

It was surmised that under and between some of the
scales of this armour there was some arrangement of
thick glasses, through which the necessary observation
could be made; and it was believed that, even if the
heavy perpendicular shots did not crush in the roof of
a crab, these glasses would be shattered by concussion.
Although this might appear a matter of slight
importance, it was thought among naval officers it
would necessitate the withdrawal of a crab from action.