The Story Of How The Submarine USS Connecticut Crashed

This is the how USS Connecticut ended up impacting a seamount, which required the crew to fight to keep the badly damaged submarine from sinking.

byJoseph Trevithick|
A screengrab from a video of the damaged USS Connecticut arriving in San Diego in December 2021 following the underwater collision two months earlier.
@SanDiegoWebCam via @WarshipCam.

Yesterday, the U.S. Navy released a long-awaited, but heavily redacted report of its investigation into the circumstances surrounding USS Connecticut hitting an uncharted seamount while sailing in the Pacific region on Oct. 2, 2021, an accident that caused extensive damage. The War Zone has now had a chance to review the entire 67-page document in detail. In the report, investigators describe how a weak command environment and lax attitudes when it came to performing key tasks ultimately put the submarine, which was also suffering issues with some of its sensor systems and other equipment, on a direct path to the accident. It also describes how the crew acted fast to save the stricken submarine that began to sink after making it to the surface after the impact. Here is our full summary of the report and its implications.

In terms of where grounding occurred, the Navy's report only confirms that Connecticut was in international waters at the time of the accident, but it has been widely reported that the submarine was somewhere in the South China Sea at the time. The unclassified portions of the investigation report reveal that the boat was conducting a humanitarian evacuation (HUMEVAC) transit at the time. The purpose of that specific transit has not been publicly disclosed, but HUMEVACs can be conducted in order to get personnel ashore for a range of reasons, including non-emergency medical care and family emergencies.

The Seawolf class submarine USS Connecticut underway in 2009. USN

The report also confirms that Navy officials at least recommended disciplinary action for Connecticut's then-Commanding Officer (CO), Cmdr. Cameron Aljilani, as well as the Executive Officer (XO) at the time, Lt. Cmdr. Patrick Cashin. There were also recommendations for nonjudicial punishments for the submarine's navigator (NAV) and assistant navigator (ANAV) at the time of the accident, along with the officer of the deck (OOD) and quartermaster of the watch (QMOW) who were on duty when the ground occurred. Chief of the Boat Cory Rodgers was recommended for formal counseling "regarding his duties and responsibilities to uphold standards." The Navy had previously announced that Aljilani, Cashin, and Rodgers had been relieved over the incident.

USS Connecticut’s underwater grounding occurred during a deployment that began in May 2021. The Navy’s report, however, highlights a number of concerning incidents even before the boat left its homeport at Naval Base Kitsap-Bremerton in Washington State. The report’s introduction goes so far as to note that command surveys and other feedback solicited from the ship’s crew by the investigating team “highlighted potential command climate issues and a generally tense relationship between the crew and the staff of Commander, Submarine Development Squadron FIVE (CSDS-5).”

USS Connecticut arrives at Naval Base Kitsap-Bremerton after a deployment in 2018. USN/Mass Communication Specialist 1st Class Amanda R. Gray

The report includes a review of events leading up to the accident tracing all the way back to when Cmdr. Aljilani assuming command of Connecticut in 2019.

“On 10 July 2020, CSDS-5 [Commander, Submarine Development Squadron Five] formally counseled the CO [commanding officer, Commander Aljilani] via a Letter of Performance,” one unredacted section notes. “The letter addressed ‘inadequate supervisory oversight, ineffective accountability practices, and superficial self-assessment.’”

Cmdr. Cameron Aljilani speaks at a ceremony marking his assumption of command of the USS Connecticut in 2019. USN

“On 16 February 2021, CSDS-5 issued a formal Letter of Instruction to the CO directing him to address the command’s overall performance, lack of improvement, and reluctance to accept feedback,” the review adds after a number of entirely redacted paragraphs.

The unclassified sections of this report do not appear to mention this, but in March 2021 it emerged publicly that Connecticut had been suffering from an infestation of bed bugs, which sailors onboard alleged had been the case for at least a year at that point. Crew morale and the general command climate had suffered as a result. You can read more about this situation here.

Then, on April 14, 2021, Connecticut smacked into a pier – a type of incident technically referred to as an allision, rather than a collision – while mooring at Naval Base Point Loma in San Diego. The submarine was there as of its pre-deployment workup.

“Before departing San Diego, Connecticut conducted a safety stand-down to address deficiencies noted by a command level critique of the pier allision,” the report into the October 2021 grounding says. “At the safety stand-down, Connecticut trained on various topics including danger recognition, risk mitigation, formality and communications, and basic watchstanding.”


The Commander of Submarine Development Squadron Five conducted a separate investigation into that accident, which was completed right before Connecticut left for its Pacific deployment. The officer assigned to lead that investigation, who is unnamed in this subsequent accident review, is said to have “opined that the allision could have been prevented with early, decisive action and recommended the CO, XO, NAV, OOD, and ANAV receive administrative or disciplinary action for dereliction of duty.” Those individuals subsequently received formal counseling.

However, while the squadron’s commanding officer concurred with the investigation and their findings, they determined that “while this investigation revealed degraded standards in navigation, planning, poor seamanship, and ineffective command and control, it represented an anomalous performance and not systematic failure.”

With the exception of the OOD, all of the individuals counseled as a result of the allusion were also recommended for disciplinary action following the underwater grounding six months later. Commander, Task Force 74 (CTF-74), which had oversight over Connecticut at the time of the October 2021 incident, told investigators that they had not been made aware of the allision or the investigation into it before the submarine arrived in their area of responsibility. CTF-74 oversees all submarine activities in the U.S. 7th Fleet area of responsibility, which covers the western Pacific Ocean and much of the Indian Ocean.

A map showing the boundaries between the areas of responsibility of the Navy's numbered fleets, including U.S. 7th Fleet (7F). via Wikimapia

Any details about what the USS Connecticut did while initially deployed in the western Pacific area are all redacted in the accident report. This is hardly surprising given the particularly sensitive nature of the Navy’s highly advanced three Seawolf class submarines. These boats, which remain the most expensive attack submarines ever built, are understood to be especially well suited to quietly cruising underneath the ice in the Arctic for protracted periods of time and for carrying out intelligence-gathering operations. The third Seawolf, USS Jimmy Carter, is actually the lone example of a unique subclass specially configured for underwater espionage activities, as you can read more about here.

An unclassified portion of the underwater accident report does describe the results of a mid-deployment check ride, where evaluators went onboard to review the crew’s performance.

“CSDS-5 evaluated Connecticut’s response to simulated loss of sounding and simulated red and yellow sounding drills as satisfactory,” the report explains. “However, the evaluation team noted that watchstanders did not fully investigate why the ship received the simulated abnormal soundings.”

A “yellow sounding” occurs when a submarine travels over the shallowest area of the Commanding Officer Safe Operating Envelope (COSOE) while operating at the maximum authorized depth. A “red sounding” is the absolute minimum acceptable safe depth defined under the COSOE and is a warning that the crew needs to take immediate action to keep the boat safe from grounding. The COSOE itself is intended to be a set of “unambiguous boundaries within which the watch section may operate without additional CO permission,” according to the report.

The unredacted portions of the report do not explain the reason or reasons why Connecticut subsequently broke off from its activities in the Pacific to conduct the HUMEVAC transit toward Okinawa or exactly where the submarine was operating at the time. However, the series of missteps that the Navy says ultimately led to the underwater grounding started right with the planning for that voyage.

The optimal path between the submarine’s initial location and Okinawa included areas for which underwater survey data was available, as well as unsurveyed areas. In addition, Cmdr. Aljilani incorrectly believed that MATT survey data was available for the transit area, in addition to data from the submarine’s onboard Voyage Management System (VMS). 

A Navy sailor operates the Voyage Management System (VMS) on the amphibious warfare ship USS San Antonio. USN/Mass Communication Specialist 2nd Class Terah L. Mollise

“MATT is a classified vector-based digital product designed specifically to support safe subsurface navigation,” according to the grounding investigation report. “Where MATT coverage exists, MATT is the recommended and preferred navigation product … for subsurface navigation.”

In addition, “the ANAV was aware that [data] on ‘swept areas’ were available in VMS, but he did not utilize this information during chart preparations,” the report notes. “During his interview, the ANAV stated he believed the soundings were “excellent” and deeper than charted based on a message from CTF-74.”

On top of that, for reasons not immediately clear, Cmdr. Aljilani made the decision to approve the use of a temporary route plan, which skips certain safety checks and approval processes built into certain systems, including the VMS. 

“A temporary route may be used at the discretion of the CO, provided the ship is operating on an approved NAVPLAN [navigation plan] and has a process for temporary route evaluation and approval,” the report says. “Connecticut does not have a process for temporary route evaluation and approval.”

The redactions make the ensuing narrative difficult to follow in places. What is clear is that Connecticut suffered, or was already experiencing, some kind of mechanical or technical issue during the transit. Cmdr. Aljilani at least expressed an interest to let CTF-74 know of the issue to try to either get replacement parts during the course of the HUMEVAC or approval to divert to Guam for in-port repairs.

These issues may or may not have been entirely related to the Connecticut’s forward and aft-mounted AN/BQQ-10 “bottom sounders,” which are among the boat’s complete array of sonar systems. The forward bottom sounder had apparently needed to be fixed once already right before deployment began and it suffered at least one issue while the boat was underway.

A composite graphic showing AN/BQQ-10 consoles displaying various data. DOD

“Ship’s force coordinated with Intermediate Maintenance Activity to troubleshoot and repair the forward bottom sounder throughout the deployment with appropriate technical assistance,” a footnote explains.

“The ship reported that although the aft bottom sounder was fully operational, its operation degraded at speeds above 16 knots,” another footnote says. “The Navy Technical Reference Publication 3-21.41.15 indicates that at a speed of 24 knots the bottom sounder transducers should operate normally up to 1400 fathoms [8,400 feet] beneath the keel before experiencing degradation.”

At some point, for reasons that are not clear from the unclassified portions of the report, the decision was made to increase the cruising speed from 16 knots to 24 knots.

The unredacted portions of the report appear to note at least two separate instances where the watchteam attempted, but failed to obtain an accurate sounding to determine Connecticut’s actual depth. On both occasions, investigators say the QMOW failed to then take appropriate action. Eventually, the XO, Lt. Cmdr. Cashin, was summoned to the bridge.

A picture showing sailors working onboard the USS Connecticut from years before the accident. USN

Connecticut did not properly mark two ‘underwater danger/underwater hazard’ locations or five areas of ‘discolored water’ as navigation hazards [on the VMS] while navigating southeast of them along the temporary route,” according to the report. In the lead up to the grounding, “the ANAV directed the QMOW to remove the red ‘stay out’ area. The ANAV did not give the QMOW a reason for his order.”

The unredacted portions of the report then note a series of discrepancies between the sounding data collected and information from the navigation charts prepared for the temporary route plan. Members of the watchteam subsequently discussed employing the submarine’s fathometer in an unsecured mode to try to secure a more accurate reading. This was an issue because of the boat’s so-called “emission control” state at the time. Emission control refers to limits that are placed on what kinds of signals Navy ships and submarines can emit in order to limit a vessel’s potential detection. For submarines, staying as “quiet” as possible in all regards is essential to surviving in combat, as well as to successfully completing various sensitive operations during peacetime and just generally remaining undetected.

Whether or not an unsecured sounding was performed or not is unclear. “The OOD stated he was concerned with the shallower-than-expected soundings but that he did not assess a need to take aggressive action,” the report notes. “The OOD did not consider ordering a lower speed.”

The last unredacted entry in the report’s narrative before the underwater grounding says “the Sonar Supervisor identified a trace near the bow. The trace was classified as biologics [a sea creature or other underwater fauna]. The Sonar Supervisor stated there were no other contacts.”

From the details included in report, the events immediately following Connecticut’s impact into the seafloor were chaotic, at least to some degree. The Diving Officer of the Watch (DOOW) twice did not hear or acknowledge orders from the OOD, the first being to change the submarine’s depth to 160 feet and then the second command to slow the speed of the ascent to keep the submarine at that depth. The submarine subsequently leveled off at a depth of 36 feet, at which point portions of the boat had broached the surface.

The report also notes that “the Digital Electromagnetic Log (EDML) lost indications” and that the “sonar reported severe degradation from the spherical array,” as a result of the accident. The latter point aligns fully with pictures and video of the damaged Connecticut that subsequently emerged showing severe damage to the bow where the spherical sonar array is held.

Once on the surface, the crew had to deal with the fact that the ship was not deballasting properly and was beginning to sink back down. Keeping the ship moving forward, despite the extent of the damage still not being known, helped it remain steady. An emergency, low-pressure blow of the main ballast tanks was eventually ordered.

While this was happening, “a watchstander incorrectly reported a propulsion lube oil (PLO) rupture in the Engine Room,” the report notes. This turned out to be spilled cooking oil that had been stored in the submarine's Shaft Alley.

Pumping of water out of the submarine’s ballast system continued to the point that “the number two trim pump motor controller glowed red and smoked,” which was “called away as an electrical fire.”

The report reiterated, as the Navy repeatedly said after disclosing the accident, that Connecticut’s nuclear reactor plant was never compromised.

Connecticut was eventually able to make contact with CTF-74 via the OPREP-3 event/incident reporting channel and was then ordered to head to Guam. The report confirms that the submarine’s bow dome was still attached, at least to some degree, immediately following the grounding, but that it broke away entirely during the trip to Guam.

A satellite image showing USS Connecticut pierside in Guam following the accident on Oct. 20, 2021. PHOTO © 2021 PLANET LABS INC. ALL RIGHTS RESERVED. REPRINTED BY PERMISSION

Of the 11 individuals who were injured in the accident, the report only describes two in any detail. Connecticut’s Maintenance Material Management Coordinator (3MC) hit their head and “suffered a scalp laceration and displayed symptoms of a concussion,” while “the OOD fractured his right scapula [shoulder blade].” 

“Nine other crew members were evaluated for minor injuries due the grounding,” the report adds. “During the transit to Guam, Connecticut identified seven Sailors who would benefit from mental health treatment. During his interview, the IDC [Independent Duty Corpsmen] stated that number grew to approximately 50 Sailors.”

Connecticut was able to make it safely to Guam after the accident, where it received an initial damage assessment and some minor repairs to ensure it was seaworthy. The submarine subsequently traveled back to Washington State by way of San Diego. The boat reportedly had to make that voyage sailing on the surface as it could not safely dive after the accident, which was likely a nightmarish experience for the crew as The War Zone has explained in the past.

“No single action or inaction caused this mishap, but it was preventable. It resulted from an accumulation of errors and omissions in navigation planning, watchteam execution, and risk management,” the report says as part of its conclusion. “Prudent decision-making and adherence to standards in any one of these three areas could have prevented the grounding.”

“A grounding at this speed and depth had the potential for more serious injuries, fatalities, and even loss of the ship,” it adds. Thankfully, “the crew put the ship in a stable condition on the surface, managed injuries and equipment damage, and transited to Guam safely and securely.”

The report’s final findings highlight the inherent risks taken from the beginning as a result of the temporary route planning, as well as subsequent failures to properly respond to indications that the situation was increasingly hazardous during the voyage itself. The Navy investigators further cite a generally lax attitude to various procedures during day-to-day operations onboard the submarine at the time.

“Failure of the CO, XO, NAV, and ANAV to identify, self-assess, and hold personnel accountable for previous navigation deficiencies led to low standards,” the report says. “The CO, XO, COB, NAV, and ANAV missed a significant opportunity for self-reflection and improvement following the pier allision in April 2021.”

“Overall, Connecticut peaked to perform at standards during inspections and evaluations as evidenced during the POMEVAL [Pre-Overseas Movement Evaluation ahead of the deployment] and mid-deployment check ride,” it adds. “In the absence of external oversight or evaluation, the CO, XO, COB, and other leaders failed to maintain day-to-day standards.”

The Navy investigators determined that the fact Connecticut’s forward bottom sounder was not working properly at the time of the accident was irrelevant. “At a speed of 24 knots, it would have provided only a few additional seconds of warning relative to the aft bottom sounder.”

“However, recurring material deficiencies with both bottom sounders may have contributed to the watchteam questioning fathometer indications and delaying action,” the report notes. “The CO should have issued a TSO [temporary standing order] to provide guidance to the watchteams on how to operate with the forward bottom sounder unavailable in DEEP modes”

The investigation found that the operations officer (OPS) at the time, who is not named, was not in any way responsible because they were not involved in a meeting regarding the navigation plan, based on their participation in a meeting that decided that 16 knots was the most appropriate cruising speed and that they were not consulted about the subsequent increase in speed. The investigators similarly assessed that the submarine’s operational safety officer (OSO) was not been properly empowered to “monitor and assess effectiveness of the ship’s operational plan.”

Of the investigation’s recommendations, seven cover disciplinary action or formal counseling for members of the crew, as are seen below. Three that are more specifically for CTF-74 are all redacted.


Three of four recommendations for Navy submarine "type commands" (TYCOM), commands that oversee various training and other administrative functions related to submarine operations, that stress improved training regarding challenging navigation scenarios and incorporation of lessons learned from this accident into future processes. 

“Reviewing any recurring deficiencies in the material condition of Seawolf-class bottom sounding equipment” is also recommended. “Personnel interviewed during this investigation indicated bottom sounder reliability is a class-wide problem.”


The report recommends that Naval Sea Systems Command (NAVSEA), in cooperation with the National Geospatial Intelligence Agency (NGA) and “VMS stakeholders,” look into improving the accuracy of underwater survey data where possible, to include more accurate details regarding known underwater hazards.


Interestingly, the last document in the list of enclosures that are part of the full report, but that were not released, is a classified “Prelimierary Collection Analysis” from the Navy’s Pathfinder class survey ship USNS Mary Sears. The War Zone has touched on the general importance of accurate underwater mapping information for submarine and other underwater operations in the past in a story about Croatian fishermen “catching” a mysterious “cube” that turned out to be a buoy from another Pathfinder, the USNS Bruce C. Heezen.

Pathfinder class survey ship USNS Mary Sears. USN

Furthermore, there’s an unclassified recommendation for NAVSEA to work to “upgrade the bottom sounder digital display coasting algorithm.” The report notes that “at the time of this grounding, the fathometer displayed a substantial and stable digital depth beneath the keel with no alarm, even as the digital trace rapidly shoaled.”

It is important to note that what we’ve learned here about Connecticut’s grounding last year is still limited and that it is difficult to truly assess the Navy’s stated conclusions based on this heavily redacted report. The unredacted portions of the report do certainly align to a great degree with the official assessments about where culpability should be placed for this incident. 

At the same time, the issues with the submarine’s sounders are interesting to note both in the context of this accident and as a rare window into the operation of the Navy’s secretive Seawolf class submarines. The War Zone has previously explored some of the ways that sonar data can potentially play into submarine collisions after an unrelated accident last year involving the Japanese submarine Soryu.

As for the USS Connecticut itself, the full extent of the damage and what the final price tag to fix the submarine might be remain unclear, though tens of millions of dollars have already been allocated to the repairs. The Navy has said that it is committed to returning it to the fleet despite the costs involved. The already small size of the Seawolf fleet makes this a top priority to ensure that the specialized capabilities these boats offer are retained to the maximum extent possible.

Whether or not more additional information about Connecticut’s grounding now that this official report has been released remains to be seen. What we do know for sure is that the submarine’s crew was thankfully able to respond quickly to the incident after it happened and prevented it from being any more serious than it was.

Above all that, it serves as a stark reminder of the very real dangers that the ‘silent service’ confronts on a daily basis, even on one of the world’s most advanced submarines.

Author's Note: The original version of this story said that spilled cooking oil from an aft galley on the submarine had been mistaken for a more serious issue after the grounding. Spilled cooking oil did cause confusion during the accident, but it was being stored in the submarine's Shaft Alley, not an aft galley.

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