Main diesel engines #3 and #4 extend
from the upper deck to the hold deck below, with the #3 engine on the starboard
side and the #4 engine on the port side. The main generators #3 and #4
are directly connected to the engines. They are located on the lower deck aft of each engine. Their rounded top can be seen as it extends just a little through the upper deck at the after end of each engine. The engines are Fairbanks-Morse 10-cylinder opposed piston engines
with an output of 1,600 shaft horsepower each. Each cylinder has two opposing
8-1/8-inch diameter pistons connected to a crankshaft at each end
(top and bottom). The power from each engine is converted to electrical
energy by the generators and was used to either charge the batteries or
to power the main propulsion motors, or both.
Located on the lower deck between the main engines is a smaller auxiliary engine. This 7-cylinder, 5-1/4 inch piston, Fairbanks-Morse engine is a smaller version of the main engines.
On the surface, even at standard speed, the engines were deafening. The noise in the compartment was so loud that the crew could only communicate with hand signals. The main air induction supplied fresh air into the compartment. The diesel engines consumed large quantities of this air, creating a strong breeze.
When the order to dive was given, the engines were instantly shut down
and all the air intakes were shut. The engines' exhausts also
had to be shut because you couldn't let water get back into the engines.
The compartment would go from roaring noise to near silence in a second. With
the diesels hot from hours of operation, the temperature would soar to
over a hundred degrees. This heat would quickly move through the entire boat. Crew members normally wore T-shirts, shorts and sandals.
The high humidity and extreme differences in temperature between the interior of the boat and the colder water of the deep caused condensation in the boat that got everything wet. This was not only tough on the crew, but also dangerous to the electrical equipment. The hull interior is lined with cork to insulate it, and there is an air conditioning system to reduce the humidity, but the boats were very hot and humid places to live and work.
It was not only hot, but the longer the boat was submerged the worse the air would get. 80 men were breathing, with each breath consuming oxygen and expelling carbon dioxide. They knew they were in trouble when there was no longer enough oxygen in the air to easily light the cigarettes that were continually smoked. At that point, oxygen would be released from compressed oxygen bottles. This helped, but also raised the internal pressure of the boat. As a last ditch effort, canisters of a carbon-dioxide absorbing chemical (caustic lithium-hydroxide) would be opened and the chemical spread on bunk covers to improve its absorption. Everyone not essential to the operation of the boat would lie down to minimize their breathing.
The boat would surface when either they had escaped the enemy, the air was so bad they could no longer function, or they ran out of battery power.
Other Features in this Compartment:
After Hull Inboard Air Induction Valve: Air entered the engine room through
this large valve in the overhead. It is connected to piping which runs along
the top of the pressure hull to the large main induction valve aft of the conning tower. The high position of the main induction valve made it less likely to be flooded when traveling on the surface.
Air Intake Silencer: Air for the main engines was drawn in through
these large cylindrical units located inboard of each engine above the
Fuel Oil Purifiers: Located aft of each engine against the after
bulkhead. They can be identified by large domed brass tops. These unit separated
water and solid sediment from fuel by centrifugal force.
Access To Main Deck: The hatch in the center of the room leads
to the main deck.