Key Points and Summary – The “Improved” Los Angeles–class—known as the 688I—was the Navy’s decisive answer to late–Cold War threats and post–Cold War strike demands.
-Building on the original SSN-688 design, the 688I added retractable bow planes and a strengthened sail for under-ice ops, quieter machinery isolation and coatings, better sonars and combat systems, and the vertical launch system for Tomahawk strikes.
-First-of-class USS San Juan (SSN-751) led a 23-boat run that saw heavy operational use, from Iraq and the Balkans to the early Global War on Terror.
-The 688I’s blend of speed, quieting, sensors, and land-attack reach set the table for Seawolf overmatch and Virginia’s modular approach.
The Improved Los Angeles–Class (688I): The Silent Bridge From Cold War To Today
By the early 1980s, the U.S. submarine force faced a sharper contest below the waves.
Newer Soviet boats—especially the Akula line—were getting quieter and deeper, shrinking the acoustic edge the Navy had enjoyed since the 1960s.
At the same time, Washington wanted its fast-attack boats to do more than stalk submarines.
Carrier battle groups needed better open-ocean escort; theater commanders wanted precise land-attack options from stealthy platforms; and Arctic operations demanded under-ice access that the earliest Los Angeles boats weren’t designed to handle.
The original SSN-688s were superb blue-water hunters, but several gaps were clear: the fairwater (sail) planes limited safe under-ice work; the combat system and sonar processing needed more power and integration; quieting had to take another leap; and the growing Tomahawk mission needed a purpose-built vertical launch capability rather than ad-hoc tube shots that could compromise load-outs.
In short, the Navy needed a more flexible, quieter Los Angeles-class submarine with actual strike and Arctic capabilities—without the cost of an entirely new class.
Designing The 688I: What Actually Changed
The 688I (“Improved Los Angeles–class”) was the Navy’s answer: a deep internal refresh that kept the hull form and reactor plant but re-engineered the business end of the boat—hydrodynamics, acoustics, sensors, combat systems, and weapons employment.
Under-Ice Capability And Bow Planes
The most visible change moved the diving planes from the sail to the bow—and made them retractable.
That shift improved low-speed maneuvering near the ice and reduced the risk of damaging appendages during through-ice surfacing. The sail itself was strengthened for Arctic work, an explicit nod to the Navy’s desire to bring attack boats comfortably into polar waters where strategic submarines operate and where access routes to the North Atlantic and Pacific can be contested.
Vertical Launch And Strike Warfare
Earlier Los Angeles boats could shoot Tomahawks through the torpedo tubes, but that’s an awkward trade—every missile in the tubes displaces a heavyweight torpedo or mine.
The improved production runs added 12 dedicated vertical launch system (VLS) cells in the bow.
With VLS, the submarine could carry a meaningful strike load without draining its torpedo magazines, and it could salvo quickly at the opening of a campaign. The result: fast-attack boats became genuine first-night strike platforms, punching open air defenses and command nodes from standoff range while remaining cloaked.
Silence And Sensors
Quieting is never one thing; it’s a thousand little things. On the 688I, you see upgraded anechoic coatings, better machinery isolation and raft mounting, refined propulsor integration, and drive-train tweaks that shave decibels across the speed regime. None of this is flashy, but in the undersea fight, every decibel is distance and every distance is life.
The sensor and combat system leap mattered just as much. The 688I boats fielded an integrated combat system suite that fused the spherical array, flank arrays, and towed arrays with new processing power and displays. That meant cleaner tracks in bad water, faster target motion analysis, and better fire-control solutions at range—exactly what you want when a duel turns on who hears, classifies, and shoots first.
Into The Fleet: The 688I Timeline
The improved run began with USS San Juan (SSN-751), the lead boat for the 23-sub 688I tranche. The “final 31” Los Angeles boats incorporated VLS, and the “final 23” (SSN-751 and higher) added the broader 688I improvements—bow planes, under-ice sail, quieting, and the integrated combat system. From San Juan through USS Cheyenne (SSN-773), the Navy steadily fielded a force that could do it all: open-ocean ASW, Arctic patrols, littoral ISR, and land attack at the push of a button.
Just as important, the 688I arrived as the Cold War ended and the strike mission surged. It was in the right place at the right time: a fast, quiet truck for torpedoes and Tomahawks that could surge globally and generate effects early in a campaign.
Combat History: From Desert Fox To Allied Force And Beyond
The 688I’s operational résumé reads like a map of post–Cold War crises.
In December 1998’s Operation Desert Fox against Iraq, 688I boats were among the platforms that opened with cruise-missile strikes on regime targets. The following spring, during NATO’s Operation Allied Force over Kosovo and Serbia, improved Los Angeles boats again contributed Tomahawk salvos as part of the opening waves.
Across the early 2000s, Los Angeles–class submarines—many of them 688Is—supported Operations Enduring Freedom and Iraqi Freedom with sustained cruise-missile fires, intelligence collection, and special operations support. The class’s combat rhythm was unglamorous but decisive: slip into a launch basket, fire when the joint force needed precise effects, then disappear to reload or retask.
One data point underscores the tempo: during the opening phase of Iraqi Freedom, U.S. submarines in the theater collectively launched a massive share of the Navy’s Tomahawks. The improved boats’ VLS cells and quiet approach lanes made them ideal first-night shooters and reliable repeat players as the air campaign unfolded. In later years, 688Is continued to deploy globally—Mediterranean, Arabian Sea, Western Pacific—conducting the blend of presence, ISR, and strike readiness that defines fast-attack utility.
The 688I In The Post–Cold War Navy
Beyond headline strikes, the 688I became the fleet’s quiet multitool. In the littorals, it could nose up to contested coastlines for periscope/ESM snapshots, deliver and recover special operations forces when tasked, and provide real-time acoustic pictures of crowded waters. In the deep ocean, it retained the speed and endurance to shadow modern adversary submarines and the sensors to hold them at risk. The combination of improved quieting and better processing meant the 688I could survive and thrive in noisy coastal zones one week and chase a quiet, fast target in blue water the next.
The boat’s training and maintenance ecosystem matured in parallel. Crews drilled relentlessly on strike mission planning, acoustic intelligence techniques, and tactical development. Shipyards and tenders learned where the 688I needed special attention to keep acoustic signatures tight throughout a long service life. The Navy also incrementally upgraded combat systems and sensors as newer processing and array tech became available—keeping the class relevant while the service awaited newer platforms.
The Los Angeles class submarine USS San Francisco (SSN 711) shown in dry dock is having repairs made on its damaged bow. A new large steel dome about 20 feet high and 20 feet in diameter was put in the place of the damaged bow. San Francisco ran aground 350 miles south of Guam Jan. 8, killing one crew member and injuring 23. U.S. Navy photo (RELEASED)
Seawolf And Virginia: Context For The 688I’s Legacy
No assessment of the 688I is complete without the two bookends that followed it: Seawolf and Virginia.
Seawolf: Overmatch At A Price
Seawolf (SSN-21 class) was what happens when you tell designers to outrun, out-dive, and out-quiet anything afloat and let them spend accordingly. In almost every tactical metric—from stealth to acoustic search volume to weapons stowage—Seawolf was a revelation. But it was also expensive, and the Cold War’s end undercut the case for a large run. Only three were built.
The crew of the Virginia-class fast-attack submarine USS Missouri (SSN 780) render honors to the Battleship Missouri Memorial following a homeport change from Groton, Connecticut. (U.S. Navy photo by Mass Communication Specialist 2nd Class Michael H. Lee/ Released)
That decision elevated the 688I’s importance: while Seawolf proved what was possible, the improved Los Angeles boats remained the day-to-day fleet—deterring, deploying, and striking. In practice, the 688I carried the bulk of the Navy’s fast-attack workload through the 1990s and 2000s, giving Combatant Commanders the underwater presence they needed at a sustainable cost.
Virginia: The Heir That Learned From 688I
Virginia (SSN-774 class) internalized the 688I’s lessons—quieting that ages well, modular sensors and payloads, and an affordable production cadence—and then pushed further. Instead of chasing raw speed and depth, Virginia emphasizes upgrade headroom and mission flexibility, from littoral ISR to seabed warfare. The class adds options like photonic masts, flexible payload interfaces, advanced sonars, and, in later blocks, the Virginia Payload Module to restore strategic strike capacity as older platforms retire.
180709-N-KC128-1131 PEARL HARBOR (July 9, 2018) – Multi-national Special Operations Forces (SOF) participate in a submarine insertion exercise with the fast-attack submarine USS Hawaii (SSN 776) and combat rubber raiding craft off the coast of Oahu, Hawaii during Rim of the Pacific (RIMPAC) exercise, July 9. Twenty-five nations, 46 ships and five submarines, about 200 aircraft, and 25,000 personnel are participating in RIMPAC from June 27 to Aug. 2 in and around the Hawaiian Islands and Southern California. The world’s largest international maritime exercise, RIMPAC provides a unique training opportunity while fostering and sustaining cooperative relationships among participants critical to ensuring the safety of sea lanes and security of the world’s oceans. RIMPAC 2018 is the 26th exercise in the series that began in 1971.` (U.S. Navy photo by Mass Communication Specialist 1st Class Daniel Hinton)
Seen in that light, the 688I is the bridge: it brought the Los Angeles design to its acoustic and mission apex, held the line operationally while Seawolf taught the edges of performance, and handed a mature, well-understood undersea trade to Virginia’s more modular future.
What Made The 688I So Effective
A few attributes explain why the improved Los Angeles class remained relevant long after the first hulls hit the water:
Balanced Design: The 688I didn’t chase a single metric. It blended speed, quieting, sensors, and payloads into a boat that could excel in both blue water and the littorals.
Strike At Scale: Twelve bow VLS cells transformed an ASW thoroughbred into a true land-attack contributor without emptying torpedo magazines.
PERSIAN GULF (March 20, 2009) The Los Angeles-class attack submarine USS Hartford (SSN 768) is underway in the Persian Gulf after a collision with the amphibious transport dock ship USS New Orleans (LPD 18). Hartford sustained damage to her sail,
but the propulsion plant of the nuclear-powered submarine was unaffected by
this collision. (U.S. Navy photo/Released)
Arctic Access: Retractable bow planes and a strengthened sail opened the polar arena to a workhorse SSN, complicating adversary planning in a region that matters more every year.
Upgrade Headroom: Integrated combat systems and array architecture gave the Navy room to roll in better processing and new towed arrays over time.
Fleet Practicality: The 688I arrived in numbers the Navy could crew, maintain, and deploy—critical when presence and surge matter as much as exquisite performance.
Where The 688I Sits Today
Even as Virginia boats dominate new construction, the Los Angeles class—chiefly the improved 688Is—remains a significant share of the fast-attack inventory.
They continue to deploy from U.S. East and West Coast hubs, integrating with carrier strike groups, supporting joint strike planning, and conducting independent undersea missions. The Navy has kept the class tactically current with combat system refreshes and array improvements, while careful maintenance preserves the acoustic gains that made the 688I special in the first place.
As adversary navies expand and undersea competition intensifies—from the Arctic to the Philippine Sea—the 688I still offers what planners prize: a proven, stealthy platform that can appear unannounced, deliver meaningful effects, and vanish.
Los Angeles-Class. Image Credit: Creative Commons.
Bottom Line
The improved Los Angeles–class gave the Navy exactly what it needed at a pivotal moment: a quieter, more capable attack submarine that could fight under the ice, stalk advanced submarines, and open wars with precision strike.
It bridged the technological gap to Seawolf’s overmatch and the strategic transition to Virginia’s modular future.
Decades on, the 688I remains the quiet, steady constant in America’s undersea story—proof that thoughtful upgrades can stretch a good design into a great one.
About the Author: Harry J. Kazianis
Harry J. Kazianis (@Grecianformula) is Editor-In-Chief and President of National Security Journal. He was the former Senior Director of National Security Affairs at the Center for the National Interest (CFTNI), a foreign policy think tank founded by Richard Nixon based in Washington, DC. Harry has over a decade of experience in think tanks and national security publishing. His ideas have been published in the NY Times, The Washington Post, The Wall Street Journal, CNN, and many other outlets worldwide. He has held positions at CSIS, the Heritage Foundation, the University of Nottingham, and several other institutions related to national security research and studies. He is the former Executive Editor of the National Interest and the Diplomat. He holds a Master’s degree focusing on international affairs from Harvard University.
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