The secret collision of the US Seawolf nuclear submarine

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The analyzes were made by Maksymilian Dura for Defence24. Their assessments, opinions and comments on the topic do not reflect the position of

WARSAW, ($1=3.96 Polish Zlotys) – The US Navy briefly reported that the USS Connecticut submarine collided with an unknown underwater object in an attempt to dispel the suspicions that there was a collision with an unknown Chinese submarine. However, it is still unknown what waters the USS Connecticut was in, that the Americans did not have proper maps and could not use anti-collision sonar.

The US Navy released a one-sentence statement on the Seawolf-type nuclear submarine USS Connecticut (SSN 22) in the South China Sea on October 2, 2021. An investigation conducted for US 7th Fleet command found that the US unit was to “land on an unexplored submarine while operating in international waters in the Indo-Pacific region.” The Commander of the 7th Fleet is now to determine whether the further action of the commander of the USS Connecticut was appropriate.

This will be difficult since the investigation did not explain why an underwater collision had occurred at all. The blame was placed on American maps, which did not inform about the existence of such high underwater obstacles at the scene. This took the responsibility off the crew, but at the same time means that:

  • The US Navy did not draw the correct conclusions from a similar accident on the USS San Francisco (SSN-711) Los Angeles-class submarine in 2005;
  • the operation of American submarines in the South China Sea can be very dangerous.

Information about inaccurate maps (if true) would undoubtedly please the Chinese who want to make the South China Sea an inner sea, with the exclusive right to exploit its underwater resources. Therefore, there is no chance that China will provide the Americans with its own, perhaps more accurate, underwater maps. The US Navy could, of course, survey the South China Sea itself, but that would require months of oceanographic vessel work. There is no money for such activity: neither the money nor the consent of the authorities in Beijing, which will certainly not allow Western countries to conduct any comprehensive research under their side.

The Chinese, however, probably did not “buy” the American explanations and are conducting their investigation of what the American nuclear submarine did that it collided “somewhere” with “some” underwater obstacle.

What is the extent of the damage to Seawolf?

So far, the size of the damage is being investigated and the cost of repairing it is estimated. Fortunately, the USS Connecticut hit the underwater mountain with its bow, thanks to which the rigid hull was not damaged (which would have been possible if the ship had rubbed its side against an obstacle over a long surface). In turn, the bow part can be likened to a car bumper, with the difference that on a submarine in the “crumple zone” (between the bow deflector and the front part of the rigid hull) there is a lot of various types of marine equipment.

So far, the Americans have only stated that the ballast tanks have been damaged, which meant that the USS Connecticut had to sail from the South China Sea to the naval base on the island of Guam for a week on the surface. Additionally, the US Navy continues to reassure us that “the nuclear reactor and the submarine’s propulsion system are undamaged.” The fore antenna system of the sonar complex – including its lower elements – must have been destroyed, so the ones most likely used to avoid collisions and mines and to periodically measure the distance to the bottom.

The condition of the main spherical sonar, which is the farthest forward element of the hydroacoustic system, is also unknown. Despite the reinforcements used, it was also probably badly damaged.

Was it possible to avoid the collision?

A submarine below the periscope depth only seems to be unable to observe the surrounding environment. Underwater, optoelectronic, and radar systems are replaced by sonar complexes using acoustic waves, which equally carefully monitor the surroundings and locate objects within the range of even several dozen nautical miles.

Photo credit: Defense Express

It is easiest in the case of “noisy” objects because sonar systems are able not only to detect a bearing on them but also to identify them (through sound analysis). It is worse with the determination of the distance, but it is also possible when using passive antenna arrays of side observation sonars or towed linear antennas, which allow for determining the position of the target using the triangulation method.

In the case of underwater obstacles that do not emit sound, the situation is much more complicated, because to detect them you need to either know where they are or locate them using active sonar. In the first case, you need accurate seabed maps as well as a precise inertial navigation system. Contrary to appearances, it is not difficult at all, because such maritime powers as the US Navy have long been creating a database of the operating areas of their ships, not only in terms of depth but also in terms of hydrological conditions (vertical temperature distribution, speed of sound propagation in water). , salinity, etc.). It is necessary, among others to allow the sonar to work accurately.

It is also not a problem to determine your position underwater without contact, for example, with the GPS, because modern submarines use very accurate inertial navigation systems, counting the distance traveled, taking into account external conditions (mainly underwater sea currents). The American Seawolf-class ships most likely have at least two such underwater navigation systems, so this could not have been the reason for a collision with anything.

It is also difficult to assume that the cause of the collision was the poorly trained crew of the USS Connecticut. All three Seawolf ships are designed for the most difficult tasks and the US Navy would certainly not allow crew members to be taken on board without the appropriate knowledge and experience.

“Connecticut hit the facility while it was submerged on the afternoon of October 2, while operating in international waters in the Indo-Pacific region,” PACFLEET Press Office said on October 7, 2021.

The simplest explanation, then, is that of the US Navy from the outset, that the maps that did not take into account the submarine that the USS Connecticut ultimately struck had failed. The problem is that such an explanation is illogical. The cause of the accident will only be found by those who explain: why anti-collision sonar was not used and what waters in the Indo-Pacific area have not yet been described on American maps.

Why was no active sonar used on the USS Connecticut?

As mentioned above, each submarine, while operating in unfamiliar waters, has the means to locate “non-noisy” underwater objects in front of and below it. These measures include, for example, active combat sonar, anti-collision sonar, anti-mine sonar, and seabed sonar.

These devices allow you to very accurately determine the bearing and distance to the detected object, but they operate according to the principle known from radars: sending an impulse (group of impulses) and then receiving the part of the energy reflected from the target. Unfortunately, this is how the submarine “sees” everything, but on the other hand, it reveals its presence. Active sonar sends an acoustic wave that can be picked up even tens of nautical miles away – alerting the enemy anti-submarine forces.

To avoid this, different types of sonar are used for different types of tasks. Again, the same principle as in the case of radars comes into play. The higher the frequency of the signal, the greater the accuracy of the measurement, but the range is shorter (and therefore also the range of its reception by the opponent). Hence, active combat sonars operate at lower, “audible” frequencies – most often in the 5-20kHz band. This allows to increase the range, but at e.g. 1 kHz requires the use of large-size antennas, which is difficult to use in the case of submarines.

In turn, in anti-collision and anti-mine sonars they already use higher frequencies, even exceeding 100 kHz. For example, a station of this type SA 9510S of the Norwegian company Kongsberg secures in one pulse (ping) at frequencies from 70 to 100 kHz, the observation sector over 120º horizontally and over 90º vertically. Apart from the selection of a higher band of the active sonar signal, its detection can be made more difficult by e.g. using a wide transmission spectrum. The pulse is then “stretched” over a wide frequency range but according to an algorithm that is only understood by a given transmitter and receiver. The signal is thus masked in some way in the ambient noise, which, however, may cause disturbances in the reception of the echo signal.

Photo credit: Defense Express

And it should be remembered that in the case of sonars it is a bit more difficult to determine the parameters of objects than in the case of a radar station because acoustic waves move in the water much slower than electromagnetic waves in the air, with different speeds (depending, for example, on the sea and the season) and not rectilinear. Hence, it is so important to know the hydrology of the sea, and therefore to have up-to-date maps of the sea on which you plan to operate.

Despite various technical improvements, active sonar is still very reluctantly used by submarine crews. And this applies not only to hydroacoustic stations that send a signal in front of the ship (eg to avoid a collision) but also to devices that send “pings” down, measuring the distance to the bottom for navigation purposes. This reluctance, however, applies only to those reservoirs where you plan to hide your own presence, e.g. by carrying out some secret mission related to the reconnaissance of the enemy, blowing up commandos, or espionage.

The failure of the active sonars to be turned on by the USS Connecticut crew meant that the ship’s mission was top secret, well worth the dangers posed by a submarine worth several billion dollars (about $ 8.5 billion at the current rate). In addition, the lack of maps with the exact shape of the bottom proves that the operation was carried out in a body of water that had not been studied by the American hydrographic services before. This may be proof that the Americans actually found themselves in the actual Chinese waters, for example following the latest submarines and surface ships mass-built in China. This is evidenced by, for example, the consistent avoidance of the term “South China Sea” and the use of the name “Indo-Pacific region” in the official communications of the US Navy when indicating the place of the accident.

Perhaps this is why the authorities in Beijing are accusing the US Navy of covering up the entire incident, asking for more detailed explanations on several occasions.

Photo credit: Defense Express

When it comes to repairing, it’s not all about money

Currently, USS Connecticut is handled by repair teams from the Puget Sound Naval Shipyard and service groups from the USS Emory S. Land (AS-39) submarine logistic support ship based in Guam. It is a vessel that is a substitute for a specialized submarine base, which, even in unprepared ports, can provide these units with electricity and water, carry out repairs and maintenance of weapons and equipment, as well as provide consumables, spare parts, medical and dental assistance, food, mail, and even legal services. For this purpose, the USS “Emory S. Land” has been set up as a small town with up to 53 different specialized stores.

Now all these repair crews are working to prepare the USS Connecticut so that it can return to the United States and undergo a full repair there. Contrary to appearances, it is not about money, but most of all about finding a shipyard that will take place to carry out the necessary renovation (e.g. a free dry dock). The schedule of US Navy shipbuilding works is so tight that it is very difficult to suddenly include an additional vessel. The inclusion of USS Connecticut in plans may therefore have an impact on other maintenance programs and tasks.

Photo credit: Defense Express

In the United States, the discussion on the need to secure the Guam base with appropriate shipbuilding infrastructure was immediately resumed – including, for example, a modern, dry dock, so that damaged ships would not later have to be transferred across the Pacific to the United States. The nearest dry dock to Guam for major repairs of submarines is located in Hawaii, and the second in the continental United States at the Puget Sound shipyard, near the USS Connecticut homeport in Bremerton, Washington.

These omissions will now extend the length of time that the US Navy will not be able to use one of its Seawolves operationally. The Americans have only three such ships, which, despite their age (they were in service in 1997, 1998, and 2005), are still considered to be the most silent ships in their class in the world (even at an underwater speed of 20 knots). Initially, they were created specifically to combat Russian submarines in the depths of the oceans. Currently, they have been adapted to perform the most secret tasks assigned to the American Navy.

It does not change the fact that it is a very well-armed submarine. It is equipped with 8 torpedo tubes of 660 mm caliber, which can be used to launch both torpedoes and Tomahawk missiles (which can take up to 50 in total). There is also space for 8 commandos on board.

Do Americans learn from their mistakes?

In all this, the Americans were very lucky. First, their ship managed to break through to Guam for several days, hiding the fact of the accident at all (including from the Chinese). Second, the collision was not serious compared to an earlier incident of this type on the Los Angeles-type USS San Francisco on January 8, 2005, 364 NM southeast of Guam Island (“near the Carolingian Islands”).

Photo credit: Defense Express

So far it is known that on the USS Connecticut “only” 1 person was injured from a crew of over 130. On the other hand, on the USS San Francisco, one officer was killed and 98 people were injured out of about 130 people on board at that time. This difference was mainly because the USS San Francisco hit the obstacle at the full underwater speed of about 35 knots (65 km / h) and was at a depth of 160 m. So the ship almost immediately stopped and the sailors ran into anything, that stood next to them (injuries mainly included bone fractures, spine injuries, head injuries, and cuts).

The automatic damage was also much greater than on the USS Connecticut (which sailed much more carefully) and included the bow ballast tanks (which had been torn apart) and the entire bow section. The part was practically completely crushed and could not be repaired. So it was replaced with a “new” one, taken from the previously withdrawn Los Angeles-class submarine – USS Honolulu (SSN-718). Fortunately, in this case, the reactor was not damaged and the ship could sail to Guam on its own, with the support of auxiliary ships.

Apart from the obvious errors in command by the commander of the ship and six other crew members, it is noteworthy that the collision in 2005 also occurred with the submarine mountain, which was not on the map used by the crew. This obstacle, however, was indicated on other maps, but it was not marked in the navigational documentation of the USS San Francisco – which was a breach of the regulations. The inconsistencies detected during periodic measurements of the distance to the bottom, which were too rare at the high speed used, were also not taken into account. The last measurement 4 minutes before the collision was, for example, at a depth of 2000 m.

This cost the Americans tens of millions of dollars to repair, and the US Navy was stripped of one submarine for four years – until April 2009, when the USS San Francisco returned to service. When the USS Connecticut will return to the line, it is not known yet.


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