Captain Jim Patton is President of Submarine Tactics & Technology of North Stonington, CT. He is a frequent contributor to these pages.
Background
Submarine Communications from Speed and Depth remains an urgent operational need with no clear technical solution. Several things have become clear, however, which promise to enable some degree of relief from the problem. First and most importantly, it has been generally accepted, at least in the short to mid-term, that there is no silver bullet solution, and that operational requirements must be met with a family of partial solutions. Secondly, meaningful analysis of the tactical issues involved highlight the fact that comms at operationally meaningful speeds and non-cavitating depths are far more important than comms at deep depths just for deep depths sake. Thirdly, regardless of foreseeable enabling technical developments, submarines will remain disadvantaged users of FORCE net assets compared to a destroyer with more than 150 dry antennas well above the air-water interface. As such, there will continue to be submarineunique techniques and procedures for operational connectivity to include continued employment of some level of broadcast means of Command and Control (C2 ) and other passive (listen only) methods.
Discussion
A key member of the family of CSD partial solutions is and will be expendable devices. Not a new concept by any means, the venerable Submarine-Launched One-Way Transmission (SLOT) buoy was used throughout the Cold War to broadcast tape-recorded messages of up to 5 minute duration to nearby Maritime Patrol Aircraft (MPA) on pre-designated VHF sonobuoy channels. The device was launched from the ubiquitous 3-inch signal ejector found on all U.S. submarines. Some later variants of this same concept used UHF to transmit directly to communications satellites.
With the development of affordable fiber optic links, what has become feasible is a tethered expendable of the same form and fit as a SLOT buoy, but which would enable two-way connectivity for dozens of minutes from hundreds of feet depth and operational meaningful speeds. A very distinct option is to exploit the mid-earth orbit of the Iridium constellation to conduct CSD with far less radiated power, easing the constraints of stored energy in the expendable device. Also, the buoy can be made capable of transmitting very large pre-loaded data files after the two-way CSD period has been completed, the tether severed, and the submarine has gone on its way. Any such two-way buoy could, of course, be used in a one-way mode in a launch and leave mode, much as was the legacy SLOT buoy. This becomes particularly attractive from an operational flexibility perspective in lieu of building a separate one-way variant if, as is projected, the cost of the spool with nearly 2 miles of fiber optic tether can be kept to a few hundred dollars.
The tactical advantages of such an expendable device need no great justification to submariners, but might not be as apparent to those who have not lived with the time and distance penalties or lost contact probabilities of coming to periscope depth while in transit or otherwise profitably employed. Also, with increased emphasis towards operating in often crowded littorals, a very real ships safety issue can be mitigated by providing other options to coming up in high contact density situations. Even given this capability in the near to mid-tenn, there will be significant challenges concerning the education of non-submariners as to the remaining limitations of submarine CSD. The initially planned loadout in the order of 100 such devices per ship sounds like a large number to submariners, the aggregate time-bandwidth product they represent is but an infinitesimal fraction of that routinely employed by other units of the joint forces who have a demonstrated ability to rapidly fill any communications pipe provided. The seemingly mundane and antiquated concept of circuit discipline wilt remain a critical aspect of operating with submarines.
Although the principle thrust of this article is to address expendables as they apply towards partial solutions to submarine CSD, once the advantage of using the 3 inch signal ejector as a convenient access to the ocean environment available on all U.S.
submarines, any number of other payloads for expendable devices come to mind. For example, a proof of concept experiment recently conducted involved connecting very affordable photonic sensors to inboard image stabilizing electronics to obtain a 360″ panoramic view of the surrounding seascape. In calm waters this view was out to several miles, and (non-intuitively) in high sea states much further, since unlike periscopes which see only the front of the next wave coming or the inside of the one that’s already there, the lightweight buoy-like object rides the top of each crest, giving frequent views of the horizon itself. Two employments of such an expendable come to mind-one for distant looks in high sea states as mentioned, and another as a safety check immediately before coming up-especially in an emergency or prior to a routine test of the Emergency Blow System.
There is another intriguing application. The Automatic Identification System (AIS) has recently been mandated for all commercial ships over 300 tons. This system constantly broadcasts a given ship’s dynamics, such as course, speed and geographic location, and also static information such as port of departure, destination and cargo summary. Imagine the tactical advantage to a submarine for ship’s safety or for Intelligence, Surveillance and Reconnaissance (ISR) to be able to passively acquire that information for all ships within 10s of miles white at speed and depth simply by launching an expendable device. Similar tethered expendable devices fitted with appropriate and increasingly inexpensive sensors could monitor other’s radar or communications emissions or sample of airborne indicators or precursors for chemical, biologic or radiological materials.
In all, the carrying of meaningful numbers of attractive variants of 3-inch expendables greatly exceeds any expected storage space available-especially since the numbers needed of each of the different variants would not be well known prior to sailing. What this combination off acts leads to is a concept of Submarine Mission Reconfigurable Expendables (SSXMR), where any number of various payloads can be mated, in real time aboard the deployed boat, to a common afterbody containing all of the common denominator hardware and standardized interfaces. This open architecture approach would stimulate future developments of even more useful
payloads and provide a convenient platform upon which to quickly field a device in response to an emergent requirement.
Conclusions
To fully exploit their intrinsic qualities of stealth. mobility, firepower and endurance. unique among combat systems in the aggregate. the modem nuclear submarine needs improved connectivity at operationally meaningful non-cavitating speeds while significantly away from periscope depth. No single technical solution is presently apparent to provide this improved connectivity, but several means exist to provide partial solutions. Predominant among these, and having the desirable attributes of being available in the short term and applicable to all U.S. submarines, are appropriately configured and fiber optic tethered expendables launched from universally existing 3-inch signal ejectors. In addition, using similar technologies. several other tactically desirable devices could be fabricated-even to the point of considering various payload modules that mate to a common afterbody to simplify stowage and logistics and facilitate further developments.
