MILITARY GEOGRAPHY
    FOR PROFESSIONALS AND THE PUBLIC

4. OCEANS AND SEASHORES

Leonard Engel
The Sea

GENERAL GEORGE C. MARSHALL, SPEAKING AS CHIEF OF STAFF, U.S. ARMY IN 1943, REVEALED, "MY MILITARY education and experience in the First World War [was] based on roads, rivers, and railroads. During the past two years, however, I have been acquiring an education based on oceans and I've had to learn all over again."¹ That made him a member of a very large club whose membership has not diminished.

Oceanography emerged as a distinctive field of military study in 1855, when U.S. Navy Lieutenant Matthew F. Maury published the first treatise on that subject, The Physical Geography of the Sea.² Findings since then have affected every naval activity from ship design to employment practices above, below, and on open waters of the Atlantic, Pacific, Indian, Arctic, and Antarctic Oceans, as well as along their littorals.

SEA WATER ATTRIBUTES

Water is one of the few substances on Earth that exists in solid, vaporous, and fluid forms, although most remains liquid. Four basic attributes of sea water are militarily important: salinity, density, stratification from surface to sea bottom, and permeability to light and sound All four are interconnected.³

SALINITY

Sea water, best described as brine, is not uniformly salty. The proportion of sodium chloride and other chemicals in solution determines salinity which, as a rule, is highest in the Horse Latitudes, which straddle 30 degrees north and 30 degrees south where dry winds encourage evaporation; less in the Doldrums astride Earth's Equator, where rainfall is abundant; and least near both poles, where melting glaciers and pack ice provide a stream of fresh water. Large river systems like the Amazon, Congo, and Mississippi also dilute the salt contents far offshore. Air temperatures and terrestrial streams condition the salinity of relatively small inland seas that directly or indirectly connect with oceans, as exemplified by the cool Baltic Sea (especially the Gulf of Bothnia near Finland), which is abnormally fresh, while the Red Sea in a torrid zone is exceptionally salty. Few major rivers feed the brackish Mediterranean, whereas the Danube, Dneister, Dneiper, and Don empty into the Black Sea.

DENSITY

High salinity increases the density (weight and mass) of sea water. So do water temperatures down to the freezing point, which approximates 28.5 ⁰F (-2 ⁰C). Surface temperatures, which average about 80 ⁰F (26.7 ⁰C) near the Equator, generally decrease 0.5 ⁰F with every degree of latitude north or south, but many anomalies obtain. Thermometers dipped in the Persian Gulf, for example, commonly register as much as 85 ⁰F (29 ⁰C), somewhat warmer than open waters around Diego Garcia 2,000 miles to the south. Pressures, which also contribute to water density, increase about 2 pounds per square foot for every 100 feet (30 meters) of descent until the weight of waters above exerts an astonishing 15 tons per square inch in the abyss.

STRATIFICATION

A much simplified representation of sea water reveals three remarkably different horizontal laminations between the ocean surface and the floor. Layer One, a watery mix well stirred by wind and waves, covers the top few hundred feet in temperate climes up to 50 degrees north and 50 degrees south latitude, although a thinner cover of warm, light water prevails in the tropics. Temperatures and salinity plummet in Layer Two, a thermocline where densities increase correspondingly until they stabilize at a depth of 5,000 to 6,000 feet (2,000 or so meters). The coldest, saltiest, and therefore the heaviest waters little influenced by seasonal change lie in Layer Three below, because the intervening thermocline acts as a barrier between top and bottom. A modified pattern exists near both poles, where cold water and low salinity dominate on the surface as well as the seabed and the absence of a permanent thermocline allows upwelling from ocean depths, as figure 7 indicates.

PERMEABILITY

Few electromagnetic emanations can penetrate sea water at great depths. Extremely low frequency (ELF) radios, the principal exception, take 15 minutes or more to transmit a three-letter message, which means that some other mode must be found to keep submarine crews abreast of football, baseball, and basketball scores. The limit of visible light is slightly more than 600 feet (200 meters) under ideal conditions, but plankton, organic debris, silt, and other suspended materials commonly reduce illumination to 50 feet (15 meters) or less along coastlines. Radar, infrared, and most radio signals rebound from the surface.

Sounds, in sharp contrast, may transmit thousands of miles under water, but directions and intensities depend on available power, geographic locations, seasonal variations, and time of day. Inorganic particles, schools of fish, gas bubbles, ship traffic, and offshore drilling scatter or absorb signals. Sounds that travel swiftly along any given duct may bounce about when they try to cross boundaries between the three horizontal sea water layers or penetrate upwelling water columns and may bend or refract as much as 15 degrees toward more favorable channels. Shadow zones that exclude sounds and convergence zones where amplifications occur further complicate sound propagation.⁴

Figure 7. Sea Water Stratification

SEA SURFACE BEHAVIOR

The uppermost layer of sea water is eternally dynamic in response to Earth's rotation, the pull of sun and moon, winds, water densities, temperatures, seismic activities, and geomagnetic influences. Currents, tides, waves, swell, and sea ice are manifestations of intense interest to military mariners and civilian policymakers who plan, prepare for, conduct, or depend upon naval operations.⁵

CURRENTS

Ocean currents, unlike waves and tides, transfer sea water long distances in endless redistribution cycles. Together with prevailing winds, they carried Christopher Columbus and his flagship the Santa Maria across the Atlantic from Europe to the New World in 1492 and took Thor Heyerdahl and the Kon-Tiki on a grand ride from Peru to the South Pacific archipelago of Tuamotu in 1947. Most naval operations have taken place in the Northern Hemisphere since Greece defeated a Persian fleet at Salamis during the Pelopponesian War in 480 B.C,⁶ but currents south of the Equator may become militarily important when least expected.

Temperature differentials set up primary circulation patterns with light, warm waters near the surface floating poleward in the Northern and Southern Hemispheres, while cold, salty waters head toward the Equator through the abyss. The direction of movement, or "set," is the course currents steer, whereas current velocities constitute "drift." Prevailing winds, which push surface water before them, start to shape a circular pattern. Earth's rotation deflects currents clockwise north of the Equator and counterclockwise to the south, with three prominent exceptions: Equatorial currents set almost due west; an underlying countercurrent sets in the opposite direction; and the Antarctic Circumpolar Current takes an easterly course around the globe unobstructed by any large land masses (map 8).

Relatively fast, narrow currents parallel the western rim of the Atlantic, Pacific, and Indian Oceans, whereas counterparts off east coasts are comparatively wide, shallow, and slow. The Gulf Stream, which is 50 miles wide (80 kilometers) and 1,500 feet deep (457 meters) near Miami, FL, drifts northward at 3 to 4 nautical miles an hour. The North Atlantic Drift, a prolongation of the Gulf Stream, spreads abnormally warm water north of the Arctic Circle past Spitzbergen and the ice-free Russian port of Murmansk until it touches Novaya Zemlya in much diluted form. Solid coastlines prevent any drift on such a scale in the North Pacific, but the cold Kamchatka Current, like the Labrador and Greenland Currents which also originate in polar regions, creates billowing fog banks on its way south when it collides with warm water headed north.

TIDES

Tides rock the oceans daily, about 12.5 hours apart, in response to gravitational tugs primarily by the moon. Spring tides about 20 percent greater than average arise twice a month when the sun reinforces lunar pull at the time of new and full moons and the Earth, moon, and sun are directly in line. Neap tides about 20 percent below average occur when the sun offsets the moon's pull at the time of lunar first and third quarters and the sun and moon are at right angles (figure 8 ).

Elaborate tables forecast daily tides for principal ports, beaches, and many lesser locales. Calculations are complex, because high and low waters everywhere arrive about 50 minutes later each day, while high and low water readings persist longer than rise and fall. Successive tides for specific spots north and south of the Equator are unequal, although alternate levels are identical. That phenomenon, oddly enough, disappears twice a month when the moon passes over the Equator. Tides register 15 to 20 percent higher than normal once a month when lunar orbits bring the moon closest to Earth (at perigee) and about 20 percent below normal once a month when the moon is farthest away (at apogee). Extreme heights occur when perigee and spring tides coincide. Tidal ranges also differ from place to place. The rise and fall of a foot or less is common along some straight line or sheltered coasts, but 50 feet (15 meters) have been recorded in New Brunswick's Bay of Fundy, a funnel-shaped basin that confines incoming slosh and rockets a 4-foot wall of water up narrow inlets at 10 to 15 miles an hour (16 to 24 kilometers per hour).

WAVES

Waves, unlike currents and tides, are whipped up entirely by winds. When winds abate, long, low, parallel waves called swell continue indefinitely, but transfer very little water from one place to another (figure 9 shows a bobbing cork that ascends each approaching wave, then slides down the reverse slope without moving far from its point of origin.) The vertical distance between the crest and trough determines wave height, the distance between successive peaks or depressions determines wave length, the speed at which each wave advances determines its velocity expressed in feet per second or nautical miles per hour, and the time it takes one crest to succeed another determines the wave period. Wave trains occasionally appear as parallel crests and troughs, but those driven by stiff breezes often

Map 8. Ocean Currents

Figure 8. Lunar and Solar Influences on Tides

overtake, pass, or overwhelm each other to form a choppy sea checkered with foam (table 4 connects wind velocities with sea states). Waves grow largest in deep water when lashed by strong steady winds over long distances--a "fetch" of 500 to 1,000 miles (800 to 1,600 kilometers) or more. Those generated in large bays never exceed a few feet no matter how hard the wind blows, whereas hurricanes and typhoons over open oceans develop superwaves that routinely top 50 feet (15 meters). A watch officer on the U.S. Navy tanker Ramapo en route from Manila to San Diego on February 7, 1933, reportedly saw a great sea rising astern "at a level above the mainmast crow's nest," and calculated its height at a record 112 feet (34 meters).⁷

Ocean waves and swell begin to slow when they reach shallow water that is about half as deep as the distance between crests (figure 10). Bottom drag then reduces spacing between waves, which rapidly increase in height and steepness until crests roll forward as breakers that pound cliffs or wash sheets of brine over flat shores where some seeps in while the rest pours back. Longshore currents slip sideways when waves strike coasts at sharp angles.

ICEBERGS AND FLOES

Icebergs can cripple or sink surface ships and submarines whose skippers are unwary, as passengers and crew of the Titanic discovered on a clear, calm night in April 1912, when that "unsinkable" luxury liner took a one-way trip to Davy Jones' locker. Glacial tongues of

Figure 9. Ocean Wave Motions and Measurements

Figure 10. Conditions Conducive to Surf

Table 4. Beaufort Wind Scale Related to Sea States

Greenland's gigantic ice cap are the source of most icebergs in the North Atlantic. Huge blocks with sharp peaks and jagged bellies break off in springtime, a process called "calving," then drift southward with ocean currents. Icebergs float, because ice is less dense than sea water, but about nine-tenths of their mass are concealed. Many tower 250 feet (76 meters) or more above the surface and spread a quarter of a mile (400 meters) or so below. Titanic's catastrophe occurred at 41^o 46' North Latitude, on a line with Madrid, Spain, although most icebergs in the Atlantic melt before they float that far south. Fewer bergs appear in the North Pacific, because "breeding" grounds are restricted, but those that break off the Antarctic ice shelf are immense, numerous, and drift farther toward the Equator than those from Greenland. Associated hazards, however, are less owing to lighter seagoing traffic.

Pack ice, which perennially covers most of the Arctic Ocean, produces flat-topped, steep-sided, tabular floes of which all proceed independently before dominant winds with narrow

strips of water known as "leads" in between. Some such floes are sufficiently large and smooth enough to accommodate medium-range cargo aircraft equipped with skis while others, buckled together by vagrant winds, feature rough surfaces that impede foot travel. Truckers at Thule Air Base, Greenland regularly drive across North Star Bay from late autumn until late spring on sea ice, which freezes 5 to 10 feet thick (2 to 3 meters) and thaws annually on the fringe of the permanent ice pack. Most floes that separate from Antarctic ice shelves in summer are much larger than any counterparts in the Northern Hemisphere; many are miles wide and 2,000 feet (600 meters) or so thick, with spectacular cliffs that tower 200 to 300 feet (60 to 90 meters) above the water.

MARINE TOPOGRAPHY

Marine topography above and below any ocean includes continental shelves, continental slopes, islands, and the abyss. Amphibious forces are essentially concerned with littorals, especially beaches, their seaward approaches, and straits, whereas "blue water" sailors factor in mountain ranges, troughs, and plains concealed under the seas.⁸

BEACHES AND APPROACHES

Beaches, which start at the shoreline and extend inland to the first marked change in topography, come in all sizes, shapes, colors, and descriptions. Those found along low-lying coasts generally are wide, long, and continuous, while others are interrupted by headlands, are confined to tiny strips by towering cliffs, or are displaced completely where mountains meet the sea. Vacationers prefer broad expanses of soft, white sand, but beaches are black on infamous Iwo Jima and some places along the Kona coast of Hawaii. Narrow strands at Nice, France, and other ritzy resorts on the Côte d'Azur are strewn with pebbles, cobblestones, and boulders. Mud deposits are by no means unusual.

Militarily useful beach studies address offshore conditions and exits inland, with particular attention to water depths, bottom gradients, obstructions, tides, currents, surf, and dominant terrain ashore (figure 11). Lengths must be adequate for amphibious forces of appropriate size, normally a battalion landing team, although tactical situations may demand larger or smaller formations. Task force commanders regularly subdivide very long beaches into segments code-named, for example, Red, White, and Blue, even Red 1, Red 2, Red 3 if necessary. Widths should afford ample room for essential command/control and logistical shore parties on dry ground above the high water mark. Beyond that, beaches ideally display the following characteristics:

• Water offshore is deep enough for transport ships to operate as near the beach as tactical situations prudently allow.
• Final approaches are free of sandbars, banks, shoals, reefs, offshore islands, rocky outcroppings, and other obstacles..
• Channel configurations discourage mining.
• Beach gradients allow amphibious landing ships and craft to discharge troops and loads on dry ground near the high water mark.
• The sea bottom and beach both are firm enough to support wheeled and tracked vehicles where dry landings are infeasible.
• Adequate landing zones are available ashore for helicopters.
• Defenders lack dominating terrain that overlooks landing beaches.
• Multiple exits of ample capacity lead from the beach to initial military objectives inland.

Figure 11. A Typical Beach Profile

Seaward approaches generally are gentle wherever shores are sandy and flat, whereas rocky coastlines tend to drop off more sharply. Beaches backed by high ground almost always abut deep water, but those at the base of cliffs habitually are littered with boulders visible only at low tide, if at all. Trucks fight for traction in dry, shifting sands on level shores; pebble and cobblestone beaches bear heavy loads, but roll so freely that tanks and other tracked vehicles slide; mud beaches often seem bottomless. Damp sand, in contrast, provides the best surface for amphibious operations. Dunes formed from fine to medium-sized wind-blown sand rarely rise more than 20 to 100 feet (5 to 30 meters) above high water, although some measure three times that high. Those that are even partly covered with vegetation are relatively firm and therefore traffickable. So are low ridges that storms create when they wash debris and driftwood ashore. Broad coastal plains behind beaches afford ample maneuver room and alternative avenues inland, provided the footing is solid, but boundaries that troops on the ground can easily find are hard to draw. Featureless terrain also affords few prominent registration points for artillery or naval gunfire, and flanks remain open. Rough topography alleviates some of those problems, but may restrict access to the hinterland.⁹

On-the-spot reconnaissance, which calls for clandestine infiltration and exfiltration capabilities along with a lengthy list of specialized skills,¹⁰ is performed whenever possible to ascertain precise characteristics of beaches, approaches, and exits before amphibious commanders approve landing plans. Superbly trained Sea-Air-Land (SEAL) teams equipped with state-of-the-art technologies most often implement such missions for the U.S. Department of Defense. Enemy armed forces are not their only adversaries--dense sea weed, sharks, barracudas, venomous sea snakes, and various fish with poisonous spines await the unwary under water.¹¹

STRAITS AND OTHER NAVAL NARROWS

Control over key straits and other natural or manmade narrows has been a basic military objective since naval warfare came into vogue well over two millennia ago, because unfriendly armed forces on one or both sides of any naval choke point may try to deny free passage to opponents.¹² Several such bottlenecks have made bold headlines in the 20th century (map 9). The Panama and Suez Canals, Gibraltar, the Red Sea's southern gate at Bab-el-Mandeb, the strait that separates Taiwan from mainland China, and the Strait of Hormuz astride sea lines of communication (SLOCs) to and from Persian Gulf oil producers are among those that have been (or still are) bones of contention.

The British Commonwealth expended 250,000 men in unsuccessful attempts to wrest the Dardanelles from the Ottoman Empire during World War I; Turkish casualties were comparable.¹³ Chechen separatists seized a ferry in the Black Sea eighty years later and threatened to blow it up in the Bosporus if Russian President Boris Yeltsin refused to lift a siege in their homeland.¹⁴ Inspiration for that audacious act may have come from former Egyptian President Gamal Abdel Nasser, who ordered subordinates to load ships with cement, then sink them in the Suez Canal during the 1967 Arab-Israeli war. Results from his standpoint were rewarding: the main channel remained closed until 1975.¹⁵

Choke points identified on map 9 helped shape U.S. and Soviet military strategy throughout the Cold War. Hunts for lone Red Octobers¹⁶ were commonplace until the Soviet Union armed its strategic nuclear submarines with long-range ballistic missiles that could attack targets from sanctuaries close to Russian coasts. Those in the Northern Fleet took cover in the Barents Sea beyond the Greenland-Iceland-Norway (G-I-N) Gaps. Counterparts with the Soviet Pacific Fleet hid in the Okhotsk bastion. Advantages, however, were by no means one sided. Soviet attack submarines and surface ships could not reach the Atlantic Ocean en masse without a fight, because NATO navies and shore-based aircraft blocked the G-I-N Gaps. Soviet Baltic and Black Sea Fleets were respectively bottled up by the Danish and Turkish Straits, which remained in NATO's hands. Occupants of the Kremlin consistently sought (but never were able) to neutralize Japan, use adjacent straits to reach open water, and close them to the U.S. Navy, which would have frustrated emergency efforts to reinforce and resupply U.N. forces in the Republic of Korea.¹⁷

CONTINENTAL SHELVES AND SLOPES

Continental shelves lie between low tide and depths of 500 to 600 feet (85 to 100 fathoms). They include shallow embayments and inland seas such as the Gulf of Mexico, Hudson Bay, the Yellow Sea, Black Sea, and the Baltic. Regions rich in food fish, oil, and mineral deposits stimulate intense economic competition, often with military overtones, because some countries press extravagant territorial claims--up to 200 miles (325 kilometers)--that international conventions have not yet negated.

Map 9. Crucial Naval Choke Points During the Cold War

Shelf widths range from 800 miles (1,300 kilometers) under arctic ice north of Siberia to narrow (even nonexistent) strips where rough terrain crowds the coast or swift currents keep sheves from forming. Most shelves are undulating plains, but low spots and protuberances are common. The Aleutian Islands festoon across the North Pacific for 1,000 miles (1,600 kilometers), while the Indonesian Archipelago stretches more than twice that far. Fringing reefs, which are coral formations attached to shore, often form in tropical climes. Like barrier reefs farther out on the shelf, they are partly submerged, parallel to the coast, and frequently block easy access from high seas to the beach, even for flat-bottomed boats. Continental slopes 10 to 20 miles wide (16-32 kilometers) begin where shelves leave off, then plunge at sharp angles until they reach the bottom which is miles below sea level in some locales. The most spectacular dropoff on Earth is located along the coast of Chile, where more than 8 vertical miles (13 kilometers) separate the Andean peak of Cerro Aconcaqua from the deepest spot in the Peru-Chile Trench fewer than 250 horizontal miles (400 kilometers) away. Undersea avalanches of stone and soupy silt occasionally race at express train speed down submerged gorges and canyons that characteristically cut into continental slopes.¹⁸

THE ABYSS AND ABOVE

Cold, dark abyssal plains covered with a thick carpet of sediments under tremendous pressure lie 15,000 to 20,000 feet (4,570-6,095 meters) below sea level. Not all of the ocean floor, however, is level. Challenger Deep, south of Guam, the most awesome of many trenches, could swallow Mount Everest without a trace. The world's longest mountain chain, known as the Mid-Ocean Ridge, winds through the Atlantic, Pacific, and Indian Oceans for 40,000 miles (64,375 kilometers) at elevations that average 5,000 to 6,000 feet (1,525-18,285 meters). Those eminances break the surface only in Iceland, but volcanic seamounts project above water in Hawaii, the Azores, and 10,000 other places large and small. Low-lying atolls that feature coral reefs around quiet lagoons are widely distributed in warm Pacific waters. Breaks in such reefs afford the only convenient avenues of arrival and departure when flats are exposed at low tide.

REPRESENTATIVE NAVAL RAMIFICATIONS

The oceans, their contents, underwater topography, and shorelines shape naval plans, programs, and operations on, above, and below the surface along the littoral as well as on high seas. This synopsis singles out three ramifications: ship designs; amphibious landings; submarine and antisubmarine warfare.

SURFACE SHIP AND SUBMARINE DESIGNS

Flotation, buoyancy, stability, and speed were essential properties of every man-of-war in olden times and will remain so eternally. Seaworthiness in the presence of ocean waves, swell, and buffeting winds was relatively easy to attain when wooden warships were fashionable, but design problems have multiplied and magnified manyfold since the first two steam-driven ironclads, the Federal ship USS Monitor and the Confederate ship CSS Virginia (originally christened the Merrimac) did battle inconclusively on March 9, 1862, in Chesapeake Bay.¹⁹

Hull dimensions, shapes, volumes, weights, and centers of gravity must be in proper proportion; performance suffers if even one of those factors is out of kilter. Surface ships float only if the submerged hull displaces a weight of water equal to the vessel's total weight, including crew, weapons, munitions, water, fuel, and other stores. Plimsoll lines drawn on cargo ships at the maximum allowable draft indicate whether they are safely loaded in tepid sea water of average salinity. Subsidiary marks account for difference in water densities, because ships ride higher or lower regardless of load when water temperatures and salt contents change (figure 12).

Figure 12. Plimsoll Line Markings

Ships underway tip up, down, and sideways around the center of flotation, which seldom coincides with centers of gravity or buoyancy. Stable hull shapes thus are the Holy Grail of every naval architect, because waves and winds not only make warships surge, sway, heave, roll, pitch, and yaw in heavy seas (figure 13), but introduce great structural stress. Ice that forms on upper decks during freezing weather also degrades stability to such an extent that poorly designed ships respond sluggishly, founder, or sink.

Surface ships must be sturdy enough to withstand slamming when flat-plated bows meet huge waves at acute angles. Forward momentum stops momentarily, the ship shudders, and vibrations from stem to stern adversely affect weapons systems. So do extreme rolling and pitching. Walls of water can damage deck-mounted equipment, wave crests that scatter electronic signals sometimes cause spurious echoes to appear on radar screens, fixed-wing and helicopter operations become impossible, and underway replenishment must be deferred regardless of need. Instability induced by winds and waves moreover may encourage motion sickness among the hardiest crew members and passengers when really foul weather strikes-- Colonel Lewis B. "Chesty" Puller, a legendary U.S. Marine, turned green in 1950 when the tail end of a typhoon rocked the ship upon which he was embarked. Mental acuity and manual dexterity suffer so greatly at such times that simple tasks become difficult. Designers consequently locate operations and control centers as well as quarters amidships, where turbulence is least pronounced.

Figure 13. Effects of Wave Action on Ship Stability

Submarines constitute a separate case, for they must sink or remain neutrally buoyant at required levels beneath the sea. Excessive buoyancy in fact would prevent rapid submersion in emergency. Crewmen pump water into ballast tanks to dive, pump part of it out to slow or terminate descent, and restore compressed air when they want to rise. Tanks fore and aft maintain submarines on an even keel, which is particularly important when they employ weapon systems or loiter at periscope depth where waters often are turbulent. Compromise designs are required to ensure effective performance, because streamlined shapes that are well suited under water are less efficient on the surface.

The corrosive effects of sea water and salt air on surface ships and submarines are pervasive and pernicious, the curse of every "swabbie" who spent most of his or her first cruise chipping paint. Superstructures and immersed hulls are under ceaseless attack. Unsightliness is the least serious problem, because metals eventually lose strength, electrical shorts occur, bolts seize up, and accretions on launch tracks cause missiles to malfunction if untended for long. Not even stainless steel is immune, so the search for antidotes and rust-resistant materials continues.

Sea weeds that foul screws and barnacles that encrust keels along with immersed instruments (such as surveillance devices) can be just as destructive as rust. Antifouling paints that slowly leach copper, tin, or mercury into sea water are somewhat protective, but their poisonous emissions are envionmentally inadvisable and hazardous to handlers. Frequent repainting with less objectionable substances must suffice until acceptable substitutes such as co-polymers become widely available.

AMPHIBIOUS LANDINGS

Amphibious warriors who wait for picture perfect beaches and approaches are apt to miss golden opportunities, while those who take calculated risks after making sound terrain analyses sometimes reap rich rewards. Island hoppers in the Pacific during World War II, for example, took fewer than 3 years to leapfrog from Guadalcanal (August 1942) to Okinawa (March 1945), even though Japanese resistance was tenacious and precious few landings took place under ideal conditions.²⁰

Two Contrasting Outcomes. British commandos armed with accurate descriptions of the German Navy stronghold at St. Nazaire, France conducted an amphibious raid in March 1942 and, against all odds, destroyed the only dry dock large enough to accommodate Hitler's superbattleship Tirpitz. The cost was high (five participants won Victoria Crosses for their valor), but ends and means were well matched. The Tirpitz, denied a home port, headed for Norway where British mini-submarines damaged it badly in 1943 before the Royal Air Force sank it in 1944 with a bevy of 6,000-pound bombs. ²¹ The bloodletting at Tarawa in November 1943 was less well planned and U.S. troops were less well equipped. More than 3,000 Marines were killed or wounded, partly because terrain intelligence was deficient. Armored amphibious tractors, the only available vehicles or landing craft able to cross that atoll's coral reef, were sufficient only for the first three waves, so follow-on forces had to wade 400-500 yards (350-450 meters) under withering fire before they reached dry land. The assault succeeded after 3 vicious days, but the value of that victory still provokes disputes.²²

The Inchon Landings. Landings at Inchon, Korea, in September 1950 (map 10), conceived by General of the Army Douglas MacArthur and conducted mainly by U.S. Marines, capitalized on surprise to achieve success with few casualties on either side even though, as one staff officer later revealed, "We drew up a list of every natural and geographic handicap--and Inchon had 'em all":²³

• The tidal range is tremendous.
• Low water exposes extensive mud flats.
• Only one narrow channel led to the landing areas.
• A fortified island blocked the final approach.
• No beaches were worthy of the name.
• A high sea wall separated all landing sites from the city.

The mission was to outflank North Korean invaders and relieve pressures on forces in the Pusan Perimeter, which was in danger of collapse. General MacArthur and his assistants seriously considered three alternatives in August 1950. Wonson, well north of the 38^th Parallel on the east coast, seemed a bit ambitious. Kunsan, well to the south on the west coast, seemed overly conservative. MacArthur elected Inchon despite objections by the Joint Chiefs of Staff (JCS),²⁴ primarily because his main political aim was to free Seoul by the end of September.

Map 10. Beaches and Approaches at Inchon

Geographic obstacles indeed were daunting. Outdated U.S. and Japanese tide tables differed significantly, but generally agreed that water would be deep enough to float landing ships, tank (LSTs), with a draft of 29 feet (9 meters) only on September 15^th, soon after sunrise and again at dusk, for periods that approximated 3 hours apiece. Schedules consequently called for the assault elements of two Marine regiments to debark 12 hours apart, with no possibility of reinforcement for first waves in the interim. Ships unable to unload troops, equipment, and supplies in that short time would be immobilized by wide, gooey mud flats that looked like solidifying chocolate but smelled like fecal matter.

LSTs and assault transports had to feel their way through tricky channels in dim light, a doubly difficult task because none at that time mounted technologically advanced navigational gear. Currents ran 6 to 8 knots (almost 10 miles per hour) when tides flowed in and out, close to the speed of available landing craft, which struggled upstream. Naval gunfire support ships had to anchor in the channel or be swept away, which made them sitting ducks for enemy artillery batteries ashore. Final approaches were so narrow there was little room to maneuver or turn around, passages were easy to mine, and one disabled ship would have blocked passage to or from final destinations. Fortunately for the amphibious task force, hostile artillery fire was desultory, no mines were found, and no ships were disabled.

Wolmi Do, a small fortified island connected to the mainland by a mile-long causeway, had to be taken on the morning tide before any ships could enter, because it dominated the harbor and waterfront in every direction. Inchon's beaches, code named Red, Green, and Blue from north to south, were small, separated from each other, bounded on the seaward side by mud flats at low tide, and backed by some combination of salt pans, piers, industrial congestion, and sea walls that had to be scaled with ladders. Two typhoons on a collision course with ports of embarkation in Japan as well as objective areas made matters worse.

Shrewd scheduling nevertheless enabled the invasion fleet to avoid the full brunt of both typhoons and catch North Korean foes flat-footed: late on D-Day General MacArthur told the JCS, "Our losses are light [21 killed, 174 wounded]," and U.N. Command Communique Number 9 announced that Seoul was recaptured on September 26, 1950, slightly ahead of schedule.²⁵ Inchon, despite geographic adversities, in short became the "jackpot spot," as Vice Admiral Arthur D. Struble, the Task Force Commander, predicted and remains a classic case study of strategic as well as tactical surprise at the U.S. Marine Corps' Amphibious Warfare School in Quantico, Virginia.

SUBMARINE AND ANTISUBMARINE WARFARE

The first recorded use of submarines as a weapon system occurred during the American Revolution when the Turtle, a one-man model with a hand-operated screw propeller, unsuccessfully sought to sink HMS Eagle, a British man-of-war, in New York harbor. The six-man Hunley flying a Confederate flag and armed with one torpedo attached to the bow, rammed and sank the Housatonic, a Federal corvette that was blockading Charleston, South Carolina, in 1864. German U-boats equipped with diesel engines, storage batteries, and self-propelled torpedoes implemented a "sink on sight" campaign in 1915 that eventually sent hundreds of Allied ships to the bottom, including the Cunard ocean liner Lusitania with 1,198 men, women, and children aboard. Submarines and antisubmarine warfare (ASW) forces have played increasingly sophisticated games of hide-and-seek ever since in a unique geographic medium.

Submarines. The ambition of every submarine skipper is to remain undetected on patrol and accomplish assigned missions unscathed. They can achieve those aspirations only if able to deceive enemy snoopers positioned to pick up the trail when they leave port, then disappear without a trace. Long-range missile submarines that maintain solitary vigils far from their targets are more difficult to find than those that must approach within torpedo range, but all submarines in motion emit energy signals, cause thermal disruptions, leave biological tracks of dying microorganisms in their turbulent wake, and disturb ultraviolet radiations in the sea. Nuclear-powered submarines ingest salt water to cool reactors, then discharge warm residue that rises to the surface where it leaves "thermal scars." Large submarines that maneuver at high speeds leave the most obvious "signatures."²⁶

Immersion in the ocean inhibits the ability of the almost "silent service" to exchange information with and receive instructions from far distant headquarters. Transmission modes that trail antennae on the surface are dead giveaways if observers are nearby; one captain who cautiously raised his periscope discovered a flock of sea gulls riding behind him as he crisscrossed an enemy convoy. One alternative is to float expendable buoys that can send preprogrammed "burst" messages with a wide choice of frequencies before they self-destruct. All options, however, are susceptible to intercepts that are traceable back to the source. Submarines can receive Very Low Frequency (VLF) traffic on set schedules at ranges that exceed 1,000 miles (1,650 kilometers) or more, provided they interrupt activities in the deep and reposition near the surface. Repeat broadcasts that give captains more than one chance to make contact foster operational flexibility, but the narrow VLF band is congested, transmissions are no faster than telegraphy, reciprocal communications are impossible, and senders cannot verify whether addressees received their messages.²⁷ Extremely Low Frequency (ELF) radios, in contrast, can send strong signals to deeply submerged submarines almost anywhere around the world. The huge installations required, however, are costly and vulnerable, procedures are ponderous, and critics oppose any such project on political, social, and environmental grounds.²⁸

Antisubmarine (ASW) Forces. ASW forces are by no means assured victory in their deadly game of hide and seek, despite the vast array of surveillance and weapon systems at their disposal. Not many optimists predict that science and technology will soon render oceans transparent, no matter how much money responsible officials devote to research and development (R&D). Acoustical sensors are most popular among many specialists who consider alternatives "unsound," but even those who pursue the full spectrum of possibilities encounter mind-boggling obstacles. Acoustical devices, which are particularly useful for long-range detection, must be submerged, remain stationary, or move slowly through the water lest hydrodynamic noises drown out incoming sounds that make it hard to differentiate legitimate indications from distractions. Ducted sounds travel great horizontal distances in salt water with little attenuation other than spreading and absorption, but bending and refraction distort signals if sensors are located in one layer and submarines in another where temperature, salinity, and pressure are quite different.²⁹

Short-range acoustic and nonacoustic surveillance devices narrow the search after long-range lookouts locate enemy submarines within a radius of 50 square miles (130 square kilometers) or so. Many complementary systems commonly conduct the search while computers record every action and skilled analysts interpret results. Aircraft may drop dozens of sonobuoys to listen at various depths, perhaps along with submersible thermometers (bathographs) to test the temperature of local water layers and estimate the quarry's likely depth. Magnetic anomaly detectors search for distortions that submarines make in Earth's magnetic field. Other equipment tries to spot electrical aberrations, bioluminescence, leaking lubricants, radioactive trace elements, and so-called "Kelvin wakes" that reach the surface.³⁰

All ASW systems now deployed or on drawing boards nevertheless have serious limitations. No current combination can overcome all geographic obstacles. Oceans, according to most well-informed opinion, thus seem likely to remain opaque pending major technological breakthroughs that few pundits predict at any early date.

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