For many years, a submariner’s principal interest in the deep seafloor environment was for its convenience as a repository for sunken ships. Seafloors, in general, were thought to be good places to avoid contact with, although some WWII boats found them useful when under depth charge attack.
Scientific interest. in the ocean depths created the need for vehicles for seafloor exploration, and the deep submergence vessel era began shortly after WWII. U.S. Navy submariners have been active participants ever since, manning TRIESTE-I and II, SEACLIFF, TURTLE, AVALON, and MYSTIC, and providing trained pilots for civilian DSVs, including ALVIN.
We said farewell to TRIESTE-II in Hay, bringing to a close a quarter century of bathyscaph service to the U.S. Navy. It started in 1957, with the Office of Naval Research (Undersea Warfare Branch) evaluation of Jacques Picard’s TRIESTE-I for oceanographic research, and continued through the years of dives to mind-boggling depths from the 35,000 foot Marianas Trench to the searches for SSNs THRESHER and SCORPION in the Atlantic. It spawned Submarine Development Group ONE, the development of DSVs and a cadre of dedicated submersible pi lots and operational support personnel, afloat and ashore. TRIESTe-I and II will be long remembered, and ar~ well-qualified to be part of the Submersible Pilot’s insignia.
Since those early times, submersible operations have become familiar to the public. Commercial DSVs support the offshore oil industry, and the exploits of DSVs employed on research and exploration activities are well covered on TV and in the printed media. There is one aspect with which not many are familiar, however; that there are very few DSVs which can reach 20,000 feet, the depth which includes over 98% of the world’s oceans. TRIESTE-II could, and she didn’t depart until SEACLIFF had been given that capability . So the U.S. Navy can still operate on the deep seafloor to explore, to inspect, to sample, to measure, to learn about the benthic environment and how to accomplish useful tasks in that remote but extensive arena.
“Benthic” is a word that describes the deep ocean environment near the seafloor. Below about 4,000 feet depth, the temperature is a nearly constant 2 0 C. At 20,000 feet, the pressure is about 600 atmospheres – almost 9, 000 psi. The currents are usually low, O. 25kt being a normal value, but they are affected by topography and have been measured as high as 2 kts. Water clarity is usually good, but not without scatterers, both sedimentary and biological, and subject to blackout when turbidity currents flow.
We are slowly learning more about the wildlife in the seabed environment, but we have a long way to go. Biofouling does not appear to be a major problem so far, and low oxygen content retards corrosion. But the environment is not uniform, nor has it been fully explored. We learn something new nearly every year that deep dives are made. Submersible operations in the deep ocean are still fascinating and still contribute to the increase of our understanding of the oceans.
All very well, you say, but what’s the connection with submarine warfare and national defense? With curent resources (one 20,000 ft. DSV, one 10,000 ft. DSV and 24,000 ft DSRVs, and no dedicated support ship capable of long distance operations) deep seafloor operations are quite limited. However, there are influences which could generate considerable expansion. Among these are 1) the changing nature of naval warfare at the sea surface, 2) advance in technology, and advances in the capabilities of other nations for operations on or near the deep seafloor.
As far back as 1969, forecasts were made that the combination of sea surveillance and long range weapon delivery could reduce the wartime effectiveness of surface forces to such an extent that major naval missions would require undersea platforms for their support. Fifteen years later we find that manned space stations and space shuttles have become commonplace, and the increased accuracy of ballistic missiles is being complemented by long range cruise missiles from several types of naval platforms. We observe that the techniques of surveilling and trailing surface ships have been developed to a high degree of reliability, thereby contributing greatly to the solution of targeting requirements for long-range weapons. Reliability and accuracy of satellite communications make it a key link in the growing threat to surface naval forces, giving opposing commanders a capability for rapid reaction to surveillance information. Weapons themselves, have greatlyimproved organic navigation, detection and CCM capabilities. The term “open sea” is taking on new meaning — more “open” to detection and attack of surface forces.
In addition to the advancesin technology that are represented in this increasing threat, we find that new capabilities are becoming possible in the undersea environment. Cumbersome sensor packages are being replaced by miniaturized components, and their signal acquisition and processing potentials are expanding by orders of magnitude. Undersea cables of large diameter and heavy armor are being overtaken by the developments of Kevlar strength members and fiber optic transmission lines, whose large bandwidths make it possible to deploy networks of undersea sensors with much more signal-carrying capacity. Drifting surface buoys are now transmitting environmental data to shore stations via satellite. Since they are capable of being anchored in the deep ocean, they offer possibilities as relay stations for seafloor data collectors. Acoustic telemetry has the potential for providing the link to the surface relay station. Seafloor power sources remain a problem, but we have tested long-term undersea operation of small nuclear reactors and they offer definite promise for the future.
The improved strength-to-weight ratio of titanium has given designers of all undersea vehicles new options, from submarines to ROVs. Even Kevlar has made its .appearance as a shallow-depth submarine hull material. With less weight required for structure, payload potential increases and with that, the flexibility and endurance of the undersea vehicle.
Communications from or near the surface to undersea vehicles near the deep seafloor will benefit from acoustic telemetry, making coordinated operations possible. Between vehicles at the seafloor, the effects of pressure on the acoustic ray paths will still limit the range of communications. Relay transponders properly placed above the seafloor, however, can make the connection between vehicles operating in a localized area.
Navigation at the seafloor within a few meters accuracy is possible now, using moored transponders for relative location, and conducting geographical grid-lock using satellite navigation at the surface. On-board navigational computers can give submersible pilots much greater capability and less dependence on directions from the surface.
When we look at. the seafloor through the eyes of other nations, we see both economic and military opportunities. Offshore petroleum resource development has moved from the shallows of the Gulf of Mexico to mile-deep wellheads in the North Atlantic. Exploration is leading to deeper depths, and technology is being challenged to provide the new capabilities required. The ability to recover manganese nodules from the vast deposits on the deep Pacific seafloor has been demonstrated. The excitement of the discovery of polymetallic sulfides near several widely separated subseafloor fracture zones is magnified by the realization that similar geologic features are to be found worldwide along the undersea edges of the moving continental and oceanic plates. Control of seafloor resources could be a factor in future economic strength, and ia consequently a key political item in the Law of the Sea deliberations.
The seafloor has been a military locale since mine warfare has existed, usually in shallow depths against surface targets. Antisubmarine mining drove the fields deeper, and now our CAPTOR weapon system has opened a new page in the mine warfare book. With the Soviets’ extensive experience in mining, they can be expected to add some pages of their own. Mine warfare in the deep ocean can lead to mine counter-measures of a novel nature.
Tracked vehicles have been operating on the seafloor since the u.s. Navy’s unmanned RUM-I in 1957 Recent press reports from Scandinavia and Japan indicate that the Soviets have developed seafloor vehicles for some form of covert activity. To determine the mission capabilities of such vehicles, we need to know whether they are manned or unmanned, autonomous or tethered. A new surveillance requirement could be developing.
What does it all add up to? Too early to tell, but look at the trends: a) more restrictions on the accomplishment of missions by surface forces particularly those involving surprise; b) increasing technical capabilities to operate on and near the seafloor, both by manned vehicles and remotely controlled systems; c) increasing pressures for discovery and exploitation of food, energy and mineral resources in the ocean; d) increasing pressures from under-developed countries to get their share of the world’s wealth; e) new military involvements in the undersea environment, particularly at the seafloor. They may not add up to Captain Nemo and the Nautilus yet, but neither do they support continuation of a near surface “status quo”. Our Navy has been a leader in developing undersea capabilities. Now other countries are pushing our lead. We need to take a look ahead at both offensive and defensive aspects of potential deep seafloor military capabilities, define our requirements and achieve the necessary levels of technical and operational performance.
Recent CNO and SECNAV ocean policy statements and requirements have created opportunities for advancement of the Navy’s capabilities in the oceans. The deep sea environment should be a prime area for that effort, and the Submarine Forces are uniquely qualified to lead the way.