October 28, 2021: In early October, an American Seawolf class SSN (nuclear attack sub), the USS Connecticut hit something while cruising submerged near China. All that has been revealed so far was that the damage was not serious but the sub did surface and slowly (SSNs move faster submerged than on the surface) take a two-week cruise back to Guam for inspection and possible repairs, depending on the extent of the damage. Satellite photos of Connecticut tied up at a pier in Guam does not reveal any visible damage. That means the damage may be along the bottom of the sub.

The navy had already revealed that eleven of the crew were injured during the collision, apparently because many crew are knocked off their feet, or seat, when there is an unexpected collision or change of direction. In past collisions that were violent and damaging, some of the crew injuries are serious, like broken bones. The current situations indicate a low-level impact. Surfacing and doing a reactor safety check and proceeding to port on the surface does not indicate a serious collision but are the current procedures for SSNs to handle situations like this. China is trying to spin this as a nuclear accident barely avoided.

This was big news in China because the sub was near China and the three Seawolfs have been assigned mainly to intelligence collecting cases. It was also a slow news day and speculative stories about nuclear powered subs are a proven attention-getter if you handle it right.

The reality is that these collisions are fairly common because three nations (U.S., Britain and France) have most of the nuclear subs and use them a lot. The nuclear submarine community has been learning some valuable lessons, and making needed changes, as a result of these collisions. As for the USS Connecticut, it most likely collided with a shipping container that fell off one of the many container ships that operate in that area and often lose some containers in bad weather. Most of these containers go to the bottom, while a few break open and some of the contents often wash up on a nearby, or distant, shore where they can, in many cases, be traced back to a container lost at sea. More dangerous for submarines are containers that, because of their cargo and container types, have enough buoyancy to linger beneath the surface at depths submerged nuclear subs operate. At these cruising depths the nukes don’t use their active (broadcasting acoustic signals like radar) sonar and instead rely on passive (listen only) sonar and electronic charts. These charts are important for subs because they are regularly updated to show newly discovered underwater reefs and seamounts that must be avoided by submerged vessels.

Navies in general, and especially those with nuclear subs, are also improving the capabilities of their passive (just listening) sonar to detect very quiet underwater objects, especially enemy subs but also naval mines or wayward shipping containers and smaller debris like waterlogged lumber that can still stay near the surface as well as whales that are not paying attention. This is not normal but seagoing mammals like whales do get sick and the result is often erratic movements, including collisions with underwater obstacles.

For one type of nuclear sub, the SSBN (nuclear ballistic missile sub), the best protection is silence and stealth. All this stealth has a downside. This was demonstrated in early 2009 when France revealed that their SSBN Le Triomphant had collided with some unknown underwater object, causing some damage to its sonar dome. At the time, the crew did not know what they had hit, and assumed that it was a cargo container. Wayward containers were already a common enough occurrence in bad weather to bother submariners. Nothing else seemed to make sense. Ten days later, after the British announced that one of their SSBNs had also collided with something underwater. Britain compared notes with the French and concluded that the two boats had run into each other. It appears that the bow (front) of the Le Triomphant scraped along the side of the SSBN HMS Vanguard. The French apparently believe that both boats were so quiet that neither boat detected the other, even after the collision. The French revealed that onboard the Le Triomphant the collision could be heard by the crew as bumping and scraping, then silence. There was a damage assessment drill, which came up clean, except for some damage to the sonar dome. That meant the sub was even less able to hear any noises coming out of the Vanguard. The Le Triomphant then proceeded on its way, only able to guess at what it had just hit. The Vanguard did the same, unaware that they had literally bumped into another stealthy SSBN.

The next generation of British, French, and American SSBNs, which are about to begin construction, were all built to be even quieter than those they are replacing. France has usually taken the lead, however slight, in this area. The other key technology is passive sonar capabilities. The U.S. pioneered this field and still does. Improved sensors and more powerful computer hardware and software make these capabilities much more effective. That did not prevent those two SSBNs from bumping into each other. The three NATO nations with SSBNs do have some procedures to avoid the possibility of SSBN collisions, especially when they are leaving or returning from their bases and via crowded (with merchant ships as well as submerged subs) with traffic approaching major ports. SSBN nations don’t like to release, even to trusted allies, any details of where there SSBNs will be on each multi-month patrol but do share some general SSBN patrol info with each other to keep two or more of their SSNs and SSBNs travelling silent while submerged from being in the same general area at the same time. The three SSBN nations are also coordinating their passive detection upgrades for the next generation. No details of that are made public but based on the known trends in technology it will be possible to get better warnings about silent submerged objects in your way.

There are two other reasons for underwater submarines colliding with something unexpectedly. The most obvious, and disastrous, case of this was the American SSN USS San Francisco hitting an undersea mountain in early 2006 at full speed while submerged. It almost sank and most of the crew were injured and one died. The cause was inaccurate charts (underwater maps showing obstacles, many of them completely and perpetually submerged). San Francisco was still using paper charts, which were updated slowly. The navy had recently developed an electronic navigation management system called VMS (Voyage Management System) and it was being installed on new and existing ships and subs. VMS electronic charts could have prevented the San Francisco collision because those charts are promptly and automatically updated. The 2006 collision involved a sea mount that was spotted by satellite in 1998 and 2004. The collision would not have happened if the sub had VMS. The navy believes that several groundings over the past decade would have been avoided had VMS been installed before the collision.

The inability to update charts quickly enough was the main reason for the collision. VMS was developed from systems used on commercial ships in the 1990s. Several other navies have also made the switch to VMS. Paper charts are replaced by electronic versions stored on a hard drive with DVD backups. The electronic charts contain more information than the paper charts, and are much easier to use, and, more importantly, update. Since the 1990s, space satellites have been surveying the oceans, and providing a flood of data for updating charts. The inability to update charts quickly enough was the main reason for San Francisco hitting an undersea mountain in early 2006. If the USS San Francisco had VMS then and the electronic charts had been promptly updated (the sea mount was spotted by satellite in 1998 and 2004), the collision would not have happened. The navy believes that several groundings over the past decade would have been avoided had VMS been installed.

The cabinets full of charts won't be discarded until Smart Ship computers and terminals are installed throughout the ship, so that others who need to use those charts can access them electronically. With VMS, navigation is much easier, and accurate. The users like it, especially the younger sailors who take it for granted that all documents will be available electronically.

Finally, there is the problem of sloppiness in using proven underwater navigation techniques when dealing with potentially dangerous, or fatal, situations. This occurs when nukes surface in areas known to have heavy traffic or when operating as part of a task force where there is usually only one sub in the area. The main responsibility is on the submarine crew and collisions with friendly surface warships or commercial vessels are usually traced back to the sub crew getting sloppy with the drill for safely surfacing in situations where there may be surface ships nearby, or where you expect to reach the surface. This is still a problem that can only be solved by officers and commanders ensuring that everyone involved is always ready to surface safely.

There are no perfect or easy solutions to these collision problems, just efforts to avoid getting sloppy with training and application of methods that do make a difference.