Air Independent Propulsion equipped diesel electric submarines offer incredibly stealthy and long diving capabilities, but they have remained somewhat diminutive in size and limited in capabilities compared to their larger nuclear counterparts. Now, renowned French naval ship builder DCNS is looking to change that with their super-sized SMX-Ocean sub concept.

The SMX-Ocean's size is telling — 328 feet long and displacing 4,750 tons while surfaced (more while submerged). That makes her roughly three times the size of the innovative AIP capable Swedish Gotland Class AIP diesel electric subs (diesel electric subs are also known as SSKs) that largely introduced the modern AIP concept as a usable form of undersea propulsion.


With greater size comes much greater capability. The SMX-Ocean is aimed directly at eliminating much of the advantages of the "SSN," the multi-role nuclear attack submarine. This is done by extrapolating the latest in AIP technologies into a larger hull design. In this larger hull there is room for traditional features that were once only found on bigger and much more expensive nuclear boats, as well as others that are on the leading edge of undersea combat.

The SMX-Ocean design, which is based loosely on the French Navy's Barracudda Class SSN, is said to offer an incredible 18,000 mile range at an average of 10 knots submerged, and the ability to patrol for 90 days without tendering or coming into port for refueling and resupply.

DCNS's latest fuel cell and lithium-ion battery based AIP technology will allow these big boats to stay submerged and near entirely silent for up to 21 days at a time. With its large internal volume, the SMX-Ocean will have enough fuel and stores on-board that it will be as adapted to 'blue water' operations (open ocean) as 'brown water' operations in the coastal littoral areas. This makes them capable of missions like carrier escort, which have traditionally been conducted by nuclear boats for navies that have the capability.


As for the SMX-Ocean's combat capabilities, they mirror or even exceed those of the most modern nuclear attack subs of a similar size, and even larger in some cases. The SMX-Ocean boats are designed to pack vertical launch tubes for land and surface attack long-range cruise missiles and even anti-aircraft missiles. This is all in addition to the standard forward firing torpedo tubes, although these too are capable of deploying anti-ship, anti-sub and even anti-air weaponry. In total, this innovative new SSK design will be able to pack an incredible amount of firepower, totaling 34 missiles, mines or torpedoes. In comparison, the Virginia Class SSNs, which are nearly double displacement, carry 39 weapons.

In addition to her bristling quiver full of missiles and torpedoes, full accommodations for a team of special forces frog men, including a lockout chamber and a 'garage' for swimmer delivery vehicles and/or a dorsally mounted midget submarines are part of the initial design.

A huge part of the SMX-Ocean concept includes the use of unmanned underwater vehicles (UUVs) and unmanned air vehicles (UAVs) that can range out far from the submarine's location. There they can use active and passive sensors to help build a situational picture of the battlespace, all without putting their mothership at risk.


For instance, an UUV can be forward deployed and used tactically to search for other subs or mines using active sonar, or it can pave the way for a special operations team inserting deep into enemy territory. A sub-launched UAV will be able to provide targeting information for a standoff attack on an enemy flotilla, reconnoiter a suspect smuggling ship, or conduct over-watch for a special forces raid. All this can be done while the sub itself still remains hidden, dozens of miles away from the target in question.

A deployable 'virtual mast' system is also built into SMX-Ocean design. Basically, this is a buoy system fitted with electro-optical, signals intelligence, and even radar sensors, as well as data-link communications, that can be deployed while the sub is at great depth. Such a system can be used as a traditional periscope would, to visually survey the boat's surface surroundings and target craft if need be, or it could be used for communications, building an aerial and surface radar picture, or to relay information collected by a sub-launched UAV.

This whole "virtual mast" technology is so exciting because it largely alleviates the most vulnerable situation that an attack sub regularly puts itself in- breaking the surface of the water to prosecute an attack, communicate, or to simply see what is going on around it. The traditional periscope itself creates a radar return that many sub hunting radar systems are incredibly capable at detecting, and it is often a sub hunter's best clue as to a boat's location. In addition, all these technologies, including UUVs, UAVs and virtual masts are all expendable, as they can be abandoned on command or destroyed by the enemy without a major loss of the submarine they are supporting. Simply put, it is a much better deal losing a $2M UUV instead of a $1B+ submarine, not even counting the cost in human life.

In the SMX-Ocean, DCNS really has a lower-cost diesel-electric AIP competitor for countries that already have nuclear attack subs in inventory, and a very enticing product for countries that do not have nuclear submarine capabilities but sure would love some without the cost or infrastructure hassle associated with them. Australia in particular has big subsurface ambitions, and many other nations, especially in Asia, may see fielding an SSN like SSK as the perfect tool to counter-balance China's increasing area-denial and anti-access technologies. Western nations are also dealing with a growing Russian threat, one that small quantities of extremely expensive 'blue water' SSNs may not be able to keep up with.

The US Navy should really take a look at the SMX-Ocean, as it would be perfect fit for a low-end (comparatively) companion to their Virginia Class SSNs and their upcoming next generation fast attack nuclear submarine design. If two of these boats could be bought for the same price as a single Virginia Class, while offering the vast majority of the Virginia Class's mission set and capabilities, the Navy would be reckless not procuring them.

If 'buying French' is deemed unacceptable, and the off-the-shelf nature of the SMX-Ocean with its lack of pork cannot attain the necessary support in Congress, than at the US Navy should design and field something similar.


As mentioned in the recent Foxtrot Alpha feature on the game-changing Swedish Gotland Class, these non-nuclear multi-role subs could be forward deployed to friendly nations, and even possibly paired with the Navy's bloated Littoral Combat Ships to increase operational synergy and give the LCS more of purpose in life.

Really, the SMX-Ocean is most likely a vision of things to come in regards to subsurface warfare technology. As nuclear submarine technology becomes increasingly unaffordable for even the most wealthy states, their capabilities will have to be shared by cheaper diesel-electric AIP boats. Meanwhile, nuclear capabilities will be better reserved for the ballistic missile deterrent mission and for fast attack submarines operating under the polar icecap or on other extreme endurance missions.


As area denial and anti-access technologies continue to proliferate, putting allied surface vessels and aircraft at greater risk, more and more missions will be pushed onto stealthy submarine forces. In the US there is already a higher tasking demand than there is a supply of available submarines by a good margin. DCNS's new SMX-Ocean could be a solution to this pressing problem, as it is one that will only worsen as time goes on.

Regardless of if the US Navy gets off its nuclear high-horse or not, these near SSN sized diesel-electric AIP boats will start to appear throughout the world in coming decades, with our friends and our enemies at the helm alike. This alone will put even more demand on America and her closest allies' gold-plated nuclear attack submarine force. At some point in time the US, UK and French navies will have to come to terms with the fact that even the best submarine in the world can only be in one place at one time, and that is dockside more often than not.


In the end, the more near-silent US subs in the water doing reconnaissance, patrols, and supporting special operations the better, regardless of how they are powered.

Tyler Rogoway is a defense journalist and photographer that maintains the website Foxtrot Alpha for You can reach Tyler with story ideas or direct comments regarding this or any other defense topic via the email address