page_title: Los Angeles-class submarine
section_title: Engineering and auxiliary systems
hierarchical_section_title: Los Angeles-class submarine / Design / Engineering and auxiliary systems
caption_attribution_description: Taken during an Anti-submarine warfare (ASW) exercise for RIMPAC 2004.
context_page_description: The Los Angeles class boats are nuclear-powered fast attack submarines in service with the United States Navy. The submarines are also known as the 688 class, after the hull number of lead vessel USS Los Angeles. They represent two generations and close to half a century of the Navy's attack submarine fleet, which currently has a total of 53 fast attack submarines in all classes. As of 2020, 33 of the Los Angeles class are still in commission and 29 are retired from service. The class has more active nuclear submarines than any other class in the world.
  Of the retired boats, a few were in commission for nearly 40 years, including USS Dallas, USS Jacksonville and USS Bremerton. With a wide variance in longevity, 12 of the 688s were laid up halfway through their projected lifespans, USS Phoenix being the youngest-retired at 16 years. Another five also laid up early, due to their midlife reactor refueling being cancelled, and one was lost during overhaul due to arson. Two are being converted to moored training ships, and all others are being scrapped per the Navy's Ship-Submarine Recycling Program. A further four boats were proposed by the Navy, but later cancelled.
context_section_description: Two watertight compartments are used in the Los Angeles-class submarines. The forward compartment contains crew living spaces, weapons-handling spaces, and control spaces not critical to recovering propulsion. The aft compartment contains the bulk of the submarine's engineering systems, power generation turbines, and water-making equipment.  Some submarines in the class are capable of delivering Navy SEALs through either a SEAL Delivery Vehicle deployed from the Dry Deck Shelter or the Advanced SEAL Delivery System mounted on the dorsal side, although the latter was canceled in 2006 and removed from service in 2009.  A variety of atmospheric control devices are used to allow the vessel to remain submerged for long periods of time without ventilating, including an electrolytic oxygen generator, which produces oxygen for the crew and hydrogen as a byproduct. The hydrogen is pumped overboard but there is always a risk of fire or explosion from this process.
  While on the surface or at snorkel depth, the submarine may use the submarine's auxiliary or emergency diesel generator for power or ventilation (e.g., following a fire).  The diesel engine in a 688 class can be quickly started by compressed air during emergencies or to evacuate noxious (nonvolatile) gases from the boat, although 'ventilation' requires raising a snorkel mast. During nonemergency situations, design constraints call for operators to allow the engine to reach normal operating temperatures before it is capable of producing full power, a process that may take from 20 to 30 minutes. However, the diesel generator can be immediately loaded to 100% power output, despite design criteria cautions, at the discretion of the submarine commander on the recommendation of the submarine's engineer, if necessity dictates such actions to: (a) restore electrical power to the submarine, (b) prevent a reactor incident from occurring or escalating, or (c) to protect the lives of the crew or others as determined necessary by the commanding officer.
caption: USS Key West submerged at periscope depth off the coast of Honolulu, Hawaii in July 2004
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