The
essential function of the periscope is to give an officer conning a submarine
a view of the surrounding horizon while the vessel is submerged.
Although simple in principle, the periscope is actually a very complicated
piece of apparatus. Essentially, a periscope consists of a vertical tube
with a head prism inclined to the horizon at a 45 degree angle, a reducing
telescope to cover a wide field, and at the bottom of the tube, an enlarging
telescope and a lower prism facing the head prism and parallel to and below
it. The objectives of the two telescopes face each other. Originally the
periscopes aboard Pampanito were raised and lowered my cables powered
by electric motors. Near the end of the war this was switched to hydraulic
power. The periscopes are about forty feet long and when lowered rest on
rubber bumpers at the bottom of the pressure hull. When they are raised
they pass through packing to prevent leaking and several brass bearings
in the support housings, or shears. They are filled with dry nitrogen to
prevent fogging.
The periscopes were also used as part of the fire control system and
could be used to determine the range and bearing of a target. The after
scope, or attack scope, is fitted with an optical range finder to determine
the range to the target. The forward, or general observation scope, is
fitted with ST radar and provided very accurate target ranges.