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Fitting the VPM into the ship
The best place to insert a VPM into the ship appears to be between the normal fuel oil (NFO) bulkhead (the forward-most bulkhead of the propulsion spaces) and the operations compartment. This location would minimize disruption of the successful Virginia-class construction program. It would also avoid any alteration of the baseline Virginia-class operations compartment, with attendant operational benefits ranging from training to logistics.

The VPM area forward of the payload tubes would house auxiliary equipment needed to support the added space and payload tube operations. The second of three decks in that area could also provide reconfigurable mission space to accommodate temporary berthing for special operations personnel or to serve as a mission planning area for unmanned vehicles or other payloads. While this is only a fraction of the space an SSGN can provide for such purposes, it represents an entirely new capability for an SSN. A smaller area aft of the tubes would contain high-pressure air flasks and an enlarged storekeeper's office with dedicated stowage lockers, which are always in short supply. Access between the propulsion spaces aft and the operations compartment forward would be through the VPM's upper deck.

Middleware to link ship and payload
Supporting new payloads beyond today's Tomahawk missiles will call for new interfaces between the payload and the ship. In the VPM concept, these interfaces are known generically as "middleware," a term borrowed from the world of computer software. In a computer, middleware provides a common interface between the operating system and the many different applications the computer hosts. In the VPM concept, it would provide a common interface between the submarine and the many different payloads a VPM might carry.

Unlike computer middleware, payload middleware for a submarine must include not just data interfaces, but also connections for power and cooling, and even structures and mechanisms to support and move the payloads themselves. Like computer middleware, VPM middleware would need to use standards that are as modular as possible so it could support the widest possible range of payloads. For example, the flexible topology of the Virginia-class electronic network would enable payloads to access whatever ship data they require.

Innovations such as inductive power transfer and laser data transfer are being considered and would go a long way toward the goal of using modular standards to support diverse payloads. Inductive power transfer does not require electrical connections. Instead, it transfers electric power between the ship and payloads via magnetic fields, minimizing connector maintenance in a saltwater environment. Similarly, lasers could transfer data between the ship and payloads via small transparent windows in the payload skin. This would also avoid the need for electrical or fiber-optic cables and their maintenance.

Another example of payload middleware is a common submarine launch system. U.S. attack submarines currently carry only torpedoes, which are launched hydraulically, and encapsulated Tomahawk cruise missiles, which are ejected from the capsule with gas pressure. However, potential future payloads could range from a more advanced and higher-speed strike weapon to unmanned surveillance systems and decoys. The Navy cannot afford to acquire and support a different launch mechanism for each individual payload.

Several candidates for a common launch system are under development, among them, capsules that float to the surface, water-piercing systems that allow payloads to rise to the surface in a gas jet, and a universal launch and recovery module that mechanically lifts payloads out of the tube. These systems require further test and evaluation, but they must also be ready soon enough to support experimentation with the new payloads that are now in the works.

Some of the payload flexibility currently embodied in SSGNs like USS Georgia (SSGN 729). Photo by Petty Officer 1st Class David Mercil.
The VPM concept would give attack boats similar to USS North Carolina (SSN 777). Photo by Petty Officer 1st Class David Mercil.

An efficient strategy for innovation
The VPM concept would be an efficient way to adapt the SSN fleet for the future. It would serve as the basis for a spiral-development process that could constantly improve attack submarine capability to keep pace with changing threats and technology. By greatly increasing the payload capability of future Virginia-class boats, it would avoid all the non-recurring costs that would be involved in developing a new submarine class for that purpose. And because the design of a VPM could evolve to support new payloads with only modest, affordable changes to the baseline ship, the Submarine Force would reap the many life-cycle savings inherent in a single, large class of attack boats, some of which will remain in service well past 2060.

At the same time, evolution of the module itself would provide design work to help sustain important elements of the submarine design industrial base. Several variants of the basic VPM concept are already being evaluated. One would provide a bottom ocean interface (BOI). Another would support a special operations force (SOF) complex.

BOI hatches on the bottom of the VPM tubes would facilitate the launch and possibly the recovery of payloads like seabed sensor systems and offensive mines. Negative buoyancy would provide the launch force, simplifying arrangements in the tube. A SOF complex would have a large, side-opening door to facilitate the launch and recovery of swimmer delivery vehicles and other small manned submersibles. A side-door configuration would also be suitable for launching and recovering the large unmanned undersea vehicles that are likely to play an increasing role in undersea operations, especially in areas where the risk is too great for the submarine itself to operate.

Revolutionary potential
Beyond the initial evolutionary benefit of more than tripling the maximum Virginia Tomahawk load-out, the VPM concept offers many advantages that could be revolutionary in nature. Although a fleet of VPM SSNs would not quite match the tremendous payload capacity of today's SSNs, they would spread that capacity across an unprecedented number of submarines. The VPM concept also has the flexibility to accommodate an unprecedented variety of payloads. To name just a few, it could carry unmanned aerial and undersea vehicles for intelligence, surveillance and reconnaissance; swimmer delivery vehicles for special operations; seabed sensor arrays; and even miniature air-launched decoys (MALD) designed to jam or spoof enemy radars.

Never before has a hull plug promised payload space that could so easily be reconfigured to support new missions and new technology over a 30-year ship life. The VPM concept promises not only to enhance the Submarine Force's ability to leverage emerging technology and keep pace with evolving threats, but to dramatically expand the missions U.S. attack submarines can undertake. Building on the already formidable mission capabilities of U.S. submarines, this would give combatant commanders many new options for confronting the growing challenges to American military power.

Retired Navy Capt. Karl M. Hasslinger is a former attack submarine commander who currently serves as Electric Boat's Director of Washington Operations. John Pavlos is an Electric Boat engineering manager who leads the Virginia Payload Module development program

Some of the payload flexibility currently embodied in SSGNs like USS Georgia (SSGN 729). Photo by Petty Officer 1st Class John Parker.

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