Captain Jim Patton is a retired submarine officer who is an active consultant in submarine matters to government and industry. He commanded USS PARGO (SSN 650).
In the very successful DARPA Submarine Payloads and Sensors program that ran from 1999-2001, one of the subjects investigated for inclusion into future submarine concepts was improved access to the ocean environment from within the watertight envelope – a capability vastly improved in JIMMY CARTER (SSN23) and the SSGNs. However, the Submarine Force doesn’t consist entirely of JIMMY CARTER and SSGNs, and even if subsequent flights of VIRGINIA’s are given significantly better access to the ocean environment, the Force will consist mainly of 688s well into this new century, and it is unlikely that any new holes will be made in their hulls. What needs to be achieved in the near term then is to acquire more operational capability through existing openings.
There has already been a great deal of effort towards employing torpedo tubes for more than just torpedoes-witness the Long term Mine Reconnaissance System (LMRS) and the Mission Reconfigurable Unmanned Underwater Vehicle (MRUUV)-both involve vehicles although (being unmanned) might be losable, but because of their monetary value are certainly not expendable. A more recent development has been to greatly increase the options available to operators for true expendables launched from the venerable and ubiquitous 3-inch signal ejector. Both the range and affordability of these options has been enabled by the same Moore’s Law that is responsible for increasingly more powerful and cheaper home computers, and by dramatic reductions in the cost and producibility of reliable fiber optics.
The type of capabilities that are currently on the table for development and deployment (nominally from operational stances in the order of 400-600 feet and 10-12 knots for 10-20 minutes) include:
- Two-way IRIDIUM comms
- Two-way VHF comms
- Two-way high data rate UHF connectivity
- 360° roll-stabilized panoramic optical views
- Automatic Identification System (AIS) receiver
- Basic ESM receiver
- Global Positioning System (GPS) receiver
- Environmental data collection sensors
- Variants where two or more of the above are combined
In fact, there are so many present options (not to mention yet to be imagined applications and the probability of various special purpose variants some entities might want to employ in limited numbers) that the concept of a mission reconfigurable device has received favorable attention. In this concept, both to mitigate onboard storage and supply system problems and to motivate further innovation in payloads, a common afterbody is being developed with an open architecture analogue of non-proprietary interface upon which, at sea, the various payloads could be mated as the mission and the tactical situation warrant. For example, even though some conceivable payloads might not require some features of the common afterbody (i.e. a one-way comms buoy not requiring the fiber optic link), the total program cost would be well served by the economics of quantity and simplicity of logistic support provided by a common afterbody. Besides, as an operator having sometimes launched two legacy SLOT buoys at a time decades ago each with the same brief tape-recorded VHF message just to raise the probability that the word would get through from at least one of them, there is something to be said for having a fiber optic link to a buoy intended for only one-way or totally autonomous use just to know that the phone has been picked up on the other end or that the buoy actually reached the surface and began its intended task- at which time the link can be severed and the ship can be back on its way.
Some interesting issues have arisen as this concept has been more fully developed. One, for example, involves the speeds and depths from which the Navy directs that the devices must be capable of being launched from-all of which can be met, but at some not insignificant cost in not only monetary form, but also in weight. This additional weight degrades the positive buoyancy of the device which directly affects rise rate and also, for optical or RF applications, the freeboard at the surface which impacts the efficiency of any antennas or the visible distance to the horizon. While it is often tactically important to operate as fast and as deep as feasible while employing these expendable devices, it would not be an onerous requirement-where there are significant capability/cost advantages available to be gained-to make transient excursions to a slower/shallower stance for the brief period required for the actual launch, after which a faster/deeper condition could be reestablished.
Another issue, given the small and fixed volume available in a 3-inch device, is it containing enough stored energy to support, for instance, two-way RF comms to a geosynchronous satellite some 25,000 miles distant. Many of the attractive battery chemistries (such as the Li-ion cells that power most newer laptops) are barred or heavily restricted for submarine use. While caution is appropriate when considering using potentially hazardous material such as mercury et. al. in the closed environment of a nuclear submarine, enough periodic review of hazards versus risk management must be conducted, as was done for the Otto fuel monopropellant in Mk 48 torpedoes, to guard against missing the opportunity to obtain greater operational capabilities while accepting whatever additional safeguards are required for safety. Perhaps this is done-one would hope so. After all, the new 8 ton Li-ion battery fabricated for the ASDS has more stored energy capacity than the 126+ ton main storage batteries currently installed on U.S. submarines, and some European companies are reportedly on the verge of building and installing Li-ion main storage batteries in their diesel-electric submarines.
There are many options coming as ammunition for the 3-inch signal ejector, and still more that haven’t yet been conceived. The lessons learned and payloads developed for employment of such expendables will not only immediately serve the Submarine Force well, but will also favorably affect tactics, techniques and procedures when future submarine designs do allow for greater access to the ocean environment with larger expendables and even recoverable devices.