served 24 years in the Navy, during which time he was involved in many
aspects of Navy oceanographic activity. In 1975, he founded and chaired
the Institute for Marine and Coastal Studies at the University of
Southern California. He left that post in 1983 to devote full time to
International Maritime Inc., which he founded in 1975 and still heads.
For nearly 100 years a primary goal for ship designers has been to
increase the range and submerged-time capabilities of submarines. It was
an elusive target until the introduction of nuclear propulsion in the
mid-1950s. But nuclear propulsion was, and is, too costly for all but
five of the world's major navies.
For the other
30 or so navies in the world diesel-electric boats would remain their
only viable option. But even the most modern of today's diesel boats are
only marginally better (in submerged-time and range) than the submarines
of World Wars I and II. Development of the first practical
air-independent propulsion (AIP) systems for diesel submarines, however,
promises much greater improvements over the next 1520 years.
demands of World Wars I and II led to a major expansion of most of the
submarine fleets of the warring powers. This led in turn to greatly
increased investments in technological development. Even after World War
II, designers developed a variety of enhancements for diesel-electric
submarines--in streamlining and noise quieting, for example, in reducing
manpower requirements in the design and production of more powerful
batteries, and in snorkel improvements (for extended submerged range).
Almost all of those, and other, capability improvements were
incremental, though, and rather modest in scale.
and Safety Problems
of air-independent propulsion systems actually began during World War
II, when the Soviet Union and Germany developed AIP systems for their
submarines. The Soviet-designed AIP system used liquid oxygen and diesel
fuel to operate a closed-cycle diesel (CCD) engine that was installed in
the submarine M-401 for an experiment that lasted from 1940 to 1945.
Professor Hellmuth Walter, an engineer, developed an AIP system that
used highly concentrated hydrogen peroxide to produce steam for a
turbine-driven submarine. Towards the end of World War II the system was
installed in the newly developed Type XXVI U-boat. As with the Soviet
system, the Walter system was plagued by numerous technical and safety
problems. Safe handling of the highly unstable peroxide in the closed
space of a submarine proved to be simply too difficult and the Type XXVI
U-boats never saw combat. Moreover, because it was so late in the war
there was neither enough time nor enough resources to convert the Type
XXVIs into effective combat units.
After World War
II the Americans, British, and Soviets all obtained access to Walter's
work and attempted to extend it to a safe conclusion. In the United
States, the Navy's Engineering Experimental Station in Annapolis, Md.,
did extensive testing of a Walter Cycle AIP system. Eventually a
reduced-size system was installed in the small experimental submarine
X-1. However, by the mid-1950s the U.S. Navy had terminated this work.
Nuclear-propulsion systems were being developed and the potential value
of AIP-powered diesel submarines seemed to be no longer important.
In Britain the
Royal Navy (RN) installed a Walter Cycle plant in HMS Excalibur to test
the system under actual seagoing conditions. The results were not
encouraging. In fact, the submarine was often referred to as "HMS
Exploder." The experiments were stopped when the Royal Navy also
shifted to nuclear submarines.
Problems Than Progress
continued AIP development for 15 years after World War II. Using data
generated from their work on WWII closed-cycle diesel AIP systems, they
built 30 Quebec-class submarines (from 1953 to 1957). They gained
considerable operational experience with AIP, but the submarines--which
ran on liquid oxygen and diesel fuel--were not satisfactory in fleet
service. There were explosions, fires, and even the loss of some
submarines. Russian submariners grimly called the Quebecs
"cigarette lighters." AIP development was terminated in the
mid-1970s, and the remaining Quebecs were scrapped. They had achieved
much greater submerged endurance and range, but those gains were
cancelled out by the unsafe nature of their AIP systems.
Soviets had also (in 1952) built an experimental Walter Cycle submarine
designated Design Project 617, which entered service in 1958. An onboard
explosion put an end to the program in 1959. From then on the Soviets
also focused on nuclear propulsion--but they did carry out some further
AIP research and development (R&D) for the diesel submarines they
continued to build.
The CCD engines
and the Walter steam turbines represented sound theoretical approaches
to AIP. Increases up to 400 percent in submerged time and/or range were
possible in the better systems; however, they still could not be made
sufficiently safe for routine fleet operations. Nuclear power seemed not
only the best but also the final answer to the submariners' dream of
virtually unlimited submerged duration. Because it was such an expensive
dream, though, nuclear propulsion was limited to only a handful of
navies. Diesel boats were the only other choice available to less
affluent navies with sizable submarine fleets. But many of those navies
hoped for an affordable AIP system to be developed some day.
The problem was
that only the major navies could afford the R&D needed in this
area--and most of those navies had dropped AIP work in favor of nuclear
propulsion. Eventually, though, submarine design groups in Germany,
Sweden, and France resumed their work on AIP systems, following four
different technical approaches: fuel cell, closed-cycle diesel, Stirling
cycle engine, and steam turbo-electric.
Advances in AIP
Navy became the first to put AIP systems into its fleet operating units.
The Kockums-built AIP system was first tested on the refurbished
submarine Näcken in 1989. Today, three Gotland-class subs (Gotland,
Uppland, and Halland) are fitted with Swedish Stirling cycle engines,
which use liquid oxygen and diesel oil. The Gotlands are powered by
hybrid diesel-electric propulsion units, with the Stirling engine
supplementing the conventional diesel-electric system. The Stirling
engine turns a generator that produces electricity for propulsion and/or
to charge the vessel's batteries.
The Gotland was
delivered in 1996. Submerged endurance (without snorkeling) for the
1,500-ton submarine is 14 days at five knots. A crew of five officers
and 28 enlisted personnel is required to operate the submarine. Kockums
now offers the similar T-96 submarine for export. The "unit
cost" of the T-96 is about $100 million.
Some of today's
most advanced AIP developmental work is being carried out by the German
Submarine Consortium (GSC). This group consists of two shipyards--the
Howaltswerke-Deutsche Werft (HDW, in Kiel) and the Thyssen Nordsee Werke
(TNSW, in Emden)--plus the IKL design bureau and the Ferrostaal trading
company. Over the past 30 years the two shipyards have delivered 122
submarines to 16 navies either as new construction or as
"kits" for local production.
For the past 15
years both shipyards have been working on parallel development of two
different AIP systems. HDW offers a fuel cell (developed with Siemens
Electric), while TNSW is marketing a closed-cycle diesel engine. After
extensive prototype testing ashore, both systems were sea-tested in
19881990 on the U-1, a former German Navy Type 205 diesel-electric
The HDW fuel
cell is scheduled to enter fleet service in 2003 on GSC's new 1,800-ton
212-class submarines. This AIP system also will be a "hybrid,"
with the submarine retaining a basic diesel-electric propulsion system.
A fuel cell cannot deliver sufficient electrical output for high-speed
operations, but the conventional storage battery can (for a short period
of time, after which the fuel cell can recharge the battery as well as
provide energy for low-speed operations).
Air But Tangible Improvements
that the 212, with its crew of 27, will be able to remain submerged for
more than a month and to cruise (at four knots) for over 3,000 miles.
Four of the $250-million submarines will be delivered to the German
Navy--two built by HDW and two built by TNSW. Two also are being built
for the Italian Navy under license at Italy's Fincantieri Shipyard.
announced the availability of the 214 class, an improved version of the
212 with greater diving depth (more than 1,400 feet), a newer
dual-fuel-cell design, and a slightly larger crew of 30 officers and
men. It has been reported that Greece intends to order three of the
Nordseewerke's closed-cycle diesel system uses liquid oxygen, diesel
fuel, and argon gas to fuel its AIP system. The oxygen and argon gases
are combined to make "artificial air" for the diesel. Argon,
an inert gas, is recovered and continuously reused. The same diesel is
used as a conventional air-breathing engine for main propulsion on the
surface or when snorkeling. TNSW's CCD AIP system is considered to be
particularly cost-effective for the retrofit of existing diesel-electric
submarines, but it also can be installed in a new-construction boat.
Both HDW and
TNSW estimate that the AIP option will add only about 15 percent to the
overall cost of a newbuild submarine. To get that much added performance
for such a small addition in cost is considered quite a bargain. It also
appears that most AIP systems will require, on average, the addition of
a hull section approximately 30 feet long.
In France the
DCN International naval shipbuilding company has developed the "MESMA"
(Module d'Energie Sous-Marine Autonome) AIP steam-turbine system, which
basically burns ethanol and liquid oxygen to make the steam needed to
drive a turbo-electric generator. DCNI offers the MESMA option for its
Agosta 90B and Scorpene classes of submarines. The company claims that
its AIP option increases submarine underwater en-durance "by a
factor of 3 to 5." The design of the MESMA system permits it to be
retrofitted into many existing submarines simply by adding an extra hull
bought three Agosta-class submarines, the first of which was
commissioned earlier this year. The third one, expected to be built in
Pakistan, will be fitted with the MESMA AIP system and thus in all
likelihood become the world's first MESMA-powered submarine.
for the Future
In addition to
the builders of the four Swedish submarines and the GSC and DCNI boats,
there are other "players" who have done considerable R&D
work on AIP systems. Russia is offering a fuel-cell option for its
"improved" Kilo- and Amur-class attack submarines. None have
yet been built with an AIP system, but reports suggest that China may
add an AIP unit to one of its Project 636 Kilos.
Netherlands' RDM submarine shipyard offers its "Spectre" CCD
option for the yard's 1,800-ton Moray 1800 H submarine; none have been
built yet, but RDM estimates that a hybrid-powered Moray could remain
submerged for 20 days while cruising at two knots. Negotiations started
earlier this year to build an AIP Moray for Egypt, but as of early
November there had been no firm commitment. The average cost of a Moray
is estimated to be about $250 million.
Maritime Self-Defense Agency has undertaken studies to add AIP systems
to its latest models of diesel-electric submarines. The leading
candidate systems are the Swedish Stirling engine and the German HDW
It is estimated
that 100150 diesel submarines will be purchased in the next 10 years.
Naval experts--and shipbuilders--throughout the world are closely
monitoring the operations of the Swedish Navy's four AIP submarines and
eagerly await the first GSC-Type 212 submarine. By 2005 there should be
sufficient fleet operating experience to determine what are the most
likely operational and cost benefits that can be derived from shifting
to AIP systems. By then the unit cost for a modern diesel-electric
submarine should be between $200 million and $300 million. Paying only
15 percent more to add or retrofit an AIP unit--a relatively small cost
for greatly improved submerged performance--should be a very attractive
could be a particularly formidable threat when operating in coastal
waters, marginal ice zones, or maritime straits and other global
"choke points." Add to that the virtual certainty that new
underwater weapons will help equalize the performance disparity between
AIP boats and nuclear-powered submarines and it may well happen that the
U.S. Navy will want to reassess the desirability of developing an AIP
submarine of its own, if only to learn how to counter this new and
potentially revolutionary undersea challenge.