After Engine Room
The After Engine Room is similar to the Forward Engine Room with Number Three and Number Four main engines and generators housed within. In addition to these, the After Engine Room houses the auxiliary engine located under the platform deck between the two main engines. The auxiliary engine is a six hundred horsepower diesel and is also connected directly to an electrical generator.
Near the center of the overhead in each engine room is a large opening with a flapper valve installed to provide air for the engines in that compartment. Each of these openings is connected via two 22-inch diameter air ducts (one for each engine room) which attach at the other end to a large 36-inch intake in the bridge. This intake and its valve are placed high in the bridge superstructure so as to be well above sea water level when surfaced. This air system is known as the Main Induction. When engines are running at full speed, air entering the boat through the main induction is traveling almost at gale force.
In each engine room (in the overhead aft) is another Christmas Tree (a panel with red and green lights) that tells the Throttlemen when it is safe to start the engines. Starting these engines with the main induction closed off would quickly cause such a vacuum in the boat that the entire crew would likely have their ear drums ruptured from the rapid pressure drop.
The photo below shows two throttlemen starting a portside engine.
In the early days of the Cold War COD's "black gang" in the After Engine Room stole a pie tin from the galley and fashioned a plaque of sorts and mounted it on a bulkhead in their work space. Their handywork is still there today (see photo below).