Updated 7/7/17 to improve readability and add information.
Anyone involved in the study or practice of naval warfare can attest to the prowess of submarines. While neither the flashiest nor most “visible” components of a navy, submarines are unique in their ability to provide access to contested regions. While surface ships are easy to detect and deter, modern submarines are extremely quiet, both sonically and in terms of electromagnetic emissions. This means they can infiltrate areas that are heavily defended by anti-access/area denial (A2/AD) defenses and sensors. This article will focus on the American Virginia-class nuclear attack submarine specifically.
Surface combatants often have a hard time balancing defense and offense. If a surface vessel devotes too many launch tubes to defense, it will find itself unable to strike effectively. Conversely, if too many tubes are used for offensive missiles, the vessel may find its defenses overcome in a large scale attack. The more sophisticated and common anti-ship missiles become, the more space must be devoted to defensive armaments, leading to a reduction in offensive firepower.
Submarines offer a solution. Impervious to anti-ship missiles when submerged and generally difficult to counter, submarines have little need for defensive weaponry. However, the United States’s attack submarines are limited in their capacity to carry weapons other than torpedoes. The US Navy’s next-generation nuclear attack submarine, the Virginia-class, currently only carries 12 Tomahawk missiles in two six-missile tubes.
In addition to the Tomahawks, Virginia-class boats have heavyweight torpedoes for engaging surface ships and other subs, the primary task of hunter-killer submarines. While these torpedoes are highly lethal against ships and other submarines at close range, they are of no use against shore-based targets and their range is limited. In response to the Virginia-class’s shortcomings in missile firepower, the US Navy has decided to upgrade its Virginia-class boats with the Virginia Payload Module (VPM). The VPM is a hull module which will be spliced into future Virginia-class nuclear attack submarines, adding extra payload space which can be used for missiles as well as other large-diameter cargo.
There are important distinctions to be made between the VPM and the current missile tubes. For one, VPM tubes can handle seven Tomahawk missiles as opposed to the six housed by the current tubes. Furthermore, the current missile tubes are outside of the boat’s pressure hull, which means they cannot be accessed while the boat is underway. VPM tubes, on the other hand, are housed inside the pressure hull, allowing for easy access if the payload needs to be serviced. Lastly, the Virginia-class’s current missile tubes lack commonality with other submarine tubes already in use by the US Navy. The VPM tubes, on the other hand, are the same diameter as the tubes on the Ohio-class and its future replacement, providing commonality across the submarine fleet. The Navy’s current plan is to splice four VPM tubes into each Block IV Virginia-class boat.
Since they are wide in diameter, the VPM tubes could be used for a myriad of payloads, including unmanned undersea vehicles, or UUVs. UUVs are essentially underwater drones which can be launched from submarines, surface ships, or planes. Like their aerial counterparts, UUVs vary greatly in size and capability. The smallest ones can be easily launched from a rigid-hulled inflatable boat and possess relatively low endurance, while the largest require a large ship or submarine for launch and can operate autonomously for days, giving them remarkable capacity to patrol and gather information.
UUVs are increasingly sought after by commanders at sea. Currently, American subsurface forces are falling short of their force requirements by significant margins, a problem exacerbated when submarines are utilized to perform low-intensity operations such as signals intelligence. The submarine force thus needs unmanned systems which can carry out such mundane tasks without tying up a whole nuclear submarine. Current UUVs are launched from torpedo tubes, the small size of which limits complexity and endurance. The VPM will allow for the employment of more sophisticated large-diameter UUVs by providing a large space for stowage and maintenance. Of course, using a VPM tube for a UUV would sacrifice some missile quantity, but a VPM submarine with one UUV tube and three missile tubes would still offer a substantial improvement over the current Virginia configuration. Plus, the Navy could tailor the VPM payload based on the circumstances; a submarine traveling to perform intelligence gathering could carry four UUVs while a submarine providing deterrence could be outfitted with four Tomahawk tubes.
By virtue of its versatility, the VPM is an archetype of sorts for the US Navy’s current philosophy of modularity and expandability. For one, VPM fits into the Navy’s “distributed lethality” objective, as it places more offensive missiles on submarines, diversifying the arsenal of cruise missile platforms. It also facilitates the more mundane but increasingly common tasks: surveillance, asymmetrical duties, etc. While high-end and lower-end capabilities often cannibalize each other’s budgets, VPM shows how the two can be combined into a single solution.