At the Battle of Tarawa in the Gilbert Islands in November 1943—one of the major amphibious landings of the war—as many as 100 boats full of U.S. Marines ran up against a coral reef hundreds of yards from shore. As Marines jumped into the water and tried to make their way to the beach, Japanese fire mowed them down.

“We couldn’t see the blood, but we knew what was happening,” Charles Pase, then a 17-year-old Marine from West Virginia, recalled of what he saw from a nearby ship. “These men were being picked off by the machine guns...we could see the machine gun bullets hitting the water like raindrops.” Still, just 76 hours after the offensive to retake the island had begun, Maj. Gen. Julian C. Smith and the warriors of the 2nd Marine Division hoisted an American flag up a palm tree on Betio, a bird-shaped island at the southwest tip of the Tarawa Atoll. A lot was riding on the operation to seize the Gilberts, which was a crucial part of the Allies’ island-hopping Central Pacific prong of attack against the Japanese.

Though the United States prevailed at Tarawa, more than 1,000 Americans were killed in the fighting and more than 2,000 wounded, a toll that prompted senior commanders to investigate a question that, especially at this critical stage of the war in the Pacific, would have extraordinary consequences: What exactly went wrong?

a portrait of woman at a boat christening
Sears in 1962, christening Atlantis II for the Woods Hole Oceanographic Institution. The research ship would ultimately travel over a million miles. © Woods Hole Oceanographic Institution

Between an aerial bombardment that fell short, an uncoordinated and delayed assault against a heavily defended shore and a shortage of amphibious tractors to get across the reef, there were plenty of missteps to scrutinize. But one major blunder that turned the shoreline into a killing field was shockingly basic. Operations planners, relying on outdated nautical charts and the imperfect memories of foreign officers, had misjudged the tide.

Many of the landing craft required a minimum of four feet of water to clear the reef, and the operation plan included high tide estimates of five feet. But on November 20, 1943, the day the amphibious assault on Tarawa began, an apogean neap tide prevailed. The tide would remain at approximately three feet, one of the lowest for the year, and would barely budge for 24 hours.

A startling realization dawned on the investigating officers. They didn’t know enough about the ocean. And the lack of this intelligence—comprehensive data on tides, waves, ocean depths, bioluminescence and underwater topography—was going to cost lives, ships and equipment as the Navy expanded the Pacific campaign. If there was any hope of mastering the seas in time to stop the Axis powers, it was up to the people on the new Joint Chiefs of Staff Committee on Meteorology’s new oceanography subcommittee—and particularly to an untested, diminutive marine biologist named Mary Sears.

As one of the few women in the tradition-bound specialty of oceanography, Sears had had to surmount numerous obstacles to establish her academic career. Even then, despite impressive scientific credentials, her appointment as the Navy’s first official oceanographer did not come easily. Yet at the age of 38, this unknown plankton researcher found herself in the middle of a terrible global war providing critical advice to combat strategists—advice that countless lives depended on. Her long-neglected story, virtually forgotten today, illustrates how the nascent field of oceanography came of age and refocused its efforts on the war, and how fledgling amphibious forces grew into premier assault teams. It’s no exaggeration to say that Sears—gathering data, making top-secret calculations on the eve of battle, leading her team of scientists and analysts, including the group she called the “enlisted girls”—helped the United States and its allies achieve victory in the Pacific.

The eldest of six children, Mary Sears was born on July 18, 1905, in Wayland, Massachusetts, 18 miles west of Boston. The house where Sears grew up abutted lush Heard Pond, where she spent warm days exploring and collecting turtles and frogs. This idyllic upbringing was interrupted when Sears’ mother suddenly took ill and died in 1911. In the aftermath, Sears’ heartbroken father went to Europe, leaving the children in the care of domestic help, relatives and friends. At a young age, Sears found herself thrust into a quasi-parental role, maintaining a steady presence for her younger siblings.

Sears’ fortunes began to brighten in 1915 when she enrolled in the highly competitive Winsor School in Boston. (Upon his return, Sears’ father married her fifth-grade homeroom teacher.) Sears then entered Radcliffe College in 1923, where she managed to find mentors—and a new path of study. Most crucially, she enrolled in classes with the prominent zoologist George Howard Parker. After her first year at Radcliffe, Sears dove headlong into the sciences, taking four botany courses and four zoology courses as well as Greek and German.

Later, Henry Bryant Bigelow, a leading marine biologist of his generation, cemented Sears’ interest in marine biology when the two met at Harvard’s Museum of Comparative Zoology and Bigelow offered her a job as his research assistant. He needed help identifying plankton specimens he had collected the previous summer. They would work side by side, beginning a fruitful association that would last decades.

a brick academic building on the water.
Part of the Woods Hole campus in Massachusetts. Sears worked summers there during graduate school and went on to become one of the institution’s top scientists © Woods Hole Oceanographic Institution

Lethal Tides: Mary Sears and the Marine Scientists Who Helped Win World War II

Catherine Musemeche weaves together science, biography, and military history in the compelling story of an unsung woman who had a dramatic effect on the U.S. Navy’s success against Japan in WWII, creating an intelligence-gathering juggernaut based on the new science of oceanography.

She finished her undergraduate degree in biology in 1927 and her master’s degree in 1929. Bigelow, instrumental in the founding of the Woods Hole Oceanographic Institution (WHOI), became its first director in 1930. After Sears completed her doctorate in zoology, in 1933, she began working for Bigelow year-round, spending the fall and spring semesters at the Museum of Comparative Zoology in Cambridge and the summers in Woods Hole. Bigelow made sure his young associate met eminent scientists from around the world, forging connections she would maintain her entire career.

Still, Sears was not allowed to sail on the institution’s main research vessel, the Atlantis, because she was a woman. The prejudice against welcoming women aboard commercial or military vessels was ancient and held that women would distract male crew members and incite the wrath of the sea. Sailors, no strangers to superstition, clung to these beliefs, and even modern expedition leaders adhered to this tradition of excluding females. At WHOI, the lack of separate bathrooms for women on the Atlantis was cited to justify the policy.

Sailing around the world was how the best oceanographers made their mark. Though Sears had so far missed out on such research trips, she had nonetheless established herself as a major figure in oceanography, specializing in plankton. Eventually, Sears grew tired of depending on male colleagues to bring back specimens from their expeditions for her; for one thing, the men did not always properly label and preserve the plankton specimens they collected.

Sears’ chance to go to sea finally came in 1941, when the ornithologist William Vogt asked her help in analyzing why guano birds in Peru, who fed on anchovies from the ocean, were dying in mass numbers. Sears traveled to Peru, where she sailed around Pisco Bay and beyond for six months on a trawler with an all-male crew. Sears kept a methodical log and collected her specimens. While at sea, she learned her country had joined the war following the attack on Pearl Harbor, circumstances that made her expedition all the more risky. Nonetheless, she stayed to complete her research duties.

When Sears returned, in March 1942, she found that the war had transformed WHOI. The boardinghouses she’d once called home had been taken over by an influx of construction workers, sailors and scientists preparing for war. The harborside laboratory had been cordoned off with barbed wire fencing, and white wooden guard shacks had sprouted up. The aquarium and the seal pool on the bustling campus, once popular gathering places for summer crowds, were closed to the public until further notice.

Returning to the labs, Sears joined a group researching the barnacles and vegetation that accumulated on ship hulls. The buildup increased drag and decreased fuel efficiency by 10 percent or more during long cruises. For ships at war, where both speed and fuel were precious commodities, a solution to the bottom-fouling problem would pay substantial dividends. Sears compiled an extensive bibliography on the marine life that contributed to bottom fouling, the kind of report that could save the government millions.

While Sears spent hours bent over her desk, combing through references on undersea organisms, she couldn’t help but notice that the hallways were becoming less congested. The crowd was thinning out as men left to join the Navy. She wanted to go too.

Toward the end of 1942, “feeling very full of patriotism,” Sears applied to join the newly established Women’s Naval Reserve, the WAVES, but she failed the medical exam and was rejected because of a prior diagnosis of arthritis. Sears had no current health issues; she exercised regularly and was an excellent candidate. She might have spent the war years stuck at WHOI but for the intervention of Lt. Roger Revelle, an oceanographer from Scripps Institution of Oceanography in San Diego.

Revelle traveled to Woods Hole to meet with WHOI director Columbus O’Donnell Iselin to convince Iselin to give up one of his precious scientists to serve at the Navy’s Hydrographic Office (“Hydro”). There was only one scientist Iselin was willing to part with, only one he deemed nonessential to the pressing wartime research taking place in the lab, and that was Mary Sears.

After Revelle’s recruiting visit, Sears reapplied for a commission in the Women’s Naval Reserve but knew she could not be accepted without a medical waiver. Adm. George S. Bryan, officer-in-charge of Hydro, was also a trustee of WHOI and well acquainted with Sears’ expertise and work ethic. He knew that she was familiar with ongoing war-related research projects including the development of the bathythermograph, an instrument that could help naval vessels evade and attack the enemy. Bryan may not have known the details of this new top-secret innovation, but as a career Navy man who had fended off German attacks during World War I, he understood the impact a new technology could have on the Navy’s war strategy. He envisioned Sears as the bridge between Hydro and WHOI, analyzing crucial information that would have profound effects on the war beneath the sea. Bryan composed a recommendation for Sears’ commission while she waited in hope. On January 21, 1943, Sears received the long-awaited waiver—and a chance to serve her country.

a man in a lab setting
Fenner Chace Jr., one of Sears’ wartime colleagues, later became a senior zoologist at the Smithsonian’s National Museum of Natural History. Department of Invertebrate Zoology, NMNH, SI

Sears attended Naval Reserve Midshipmen’s School at Mount Holyoke in South Hadley, Massachusetts, one of only two locations where women could train to be naval officers. She graduated in April 1943 and started at Hydro, working alone at a desk in the Maritime Security Division, facing an avalanche of requests for data from the Army and the Navy.

All too often, charts and sailing directions, if they could be found at all, were hopelessly out of date, in some cases more than 100 years old—even for high-priority invasion targets. Some types of data were never going to be easy to obtain because of ongoing war operations that inhibited the U.S. ability to survey certain areas. Much of this data, such as local tides, currents or beach conditions for some remote locales, was not easily accessible, especially for those areas in the Pacific where the U.S. had never been to war. Sears was new to her role but could already see that the Navy needed someone who could quickly assess the information already available on the shelves of libraries and government agencies and determine what still needed to be collected.

Sears had just taken her seat as the newest member of the Joint Chiefs’ Subcommittee on Oceanography in April 1943 when her colleagues asked her to compile all available references on the surface drifts of objects in the Atlantic and Pacific oceans. The request had come after a high-profile incident involving Capt. Eddie Rickenbacker, a renowned World War I fighter ace. Rickenbacker had been on assignment for the War Department when his plane crashed in the Pacific Ocean. The crew had languished for weeks at the mercy of storms, a searing sun and the constant threat of shark attacks. On Day 20, the pilot went looking for help in one of the rafts and was picked up by a naval patrol boat. The lingering question was why had it taken three weeks to rescue the survivors, even though air traffic control had given the Navy an approximate location of where Rickenbacker had crashed.

Predicting the drift of objects such as airplane wreckage had proven to be a complicated matter. Sears tackled the assignment with her trademark focus, gathering all the published data she could find and relying on her network of experts at Woods Hole and Scripps for more. But how did she know where to look in the first place? In an age before computers and Internet searches, Sears had developed a system of filling out an index card for every article, book, newsletter or other reference she reviewed. She cross-referenced these by author and subject, filing them alphabetically in black boxes that sat on a shelf behind her desk.

In May 1943, Sears submitted The Drift of Objects under the Combined Action of Wind and Current to the subcommittee members. They endorsed her conclusions without hesitation and forwarded her monograph up the chain of command. Her report laid the foundation for initiatives that would rescue hundreds of pilots and crews lost at sea during the war—and put to rest any lingering skepticism about the capabilities of this female oceanographer.

Only weeks later, Sears welcomed Fenner Chace Jr., a crustacean expert she had met at Harvard, to the Oceanographic Unit. Chace had been working on cloth rescue maps to help downed pilots find their way to safe shores in the Pacific. Pilots could easily tuck these waterproof, handkerchief-size maps in a pocket of their flight jackets. Using his hobbyist painting skills, Chace sketched in the strength and direction of currents on these cloth maps. Sears, fresh from the drift project, assisted him with the data, the two of them combining their scientific know-how to produce new maps. While it was a major achievement for the new collaborators, their most significant contributions still lay ahead.

a woman wearing glasses
Mary Grier, one of the foremost oceanographic librarians in the nation, joined Sears in the Navy’s Hydrographic office in 1943. Courtesy of Liz Illg
a woman poses next to a hanging marlin on a dock
Another colleague of Sears’ on the Hydro staff was barnacle expert Dora Henry, who was avid about deep-sea fishing. Courtesy of Kathy Newell

Sears was already building the Oceanographic Unit into a 15-member team of oceanographers, draftsmen and women. Her core team members did not fit the profile of military oceanographer any more than Sears did. In civilian life, Chace had spent most of his time dissecting and sketching crustaceans in the catacombs of Harvard’s Museum of Comparative Zoology. Dora Henry of the University of Washington, a k a “the Barnacle Lady,” had scoured tidal pools and shoals around Puget Sound and begun to assemble an extensive collection of barnacle species; she was so famous that the author John Steinbeck even sent her barnacles he thought would interest her. Meanwhile, Mary Grier, a University of Washington librarian with an expansive knowledge of oceanographic publications, had alleged ties to the Communist Party. However unconventional this team might have been, the Navy didn’t have the time to be choosy. A series of risky amphibious missions had already been penciled into war plans.

After Pearl Harbor, the Japanese had launched a sweeping attack against the U.S. territories of Guam, Wake Island and the Philippines, and against the Dutch East Indies, Malaya and Hong Kong. But by the summer of 1942, the U.S. had scored strategic victories at the Battles of the Coral Sea and Midway that promised to give the Allies the upper hand in the Pacific. A further turning point for U.S. forces in the region came when defeated Japanese forces withdrew from Guadalcanal in February 1943. Through a grueling six-month campaign, the Allies devastated Japanese air, naval and ground forces; the attacks began with a remarkably successful landing at Guadalcanal in the Solomon Islands the previous August—the U.S.’s first amphibious attack in the Pacific. After the battle, the Japanese military had difficulty recovering: While the U.S. wartime industry was ramping up, churning out more and more aircraft carriers, destroyers, submarines and aircraft, Japan was meeting its industrial limits and suffering from a lack of raw materials. The victory allowed the Allies to continue on the offensive, intent on driving the Japanese all the way back to Japan.

Adm. Chester W. Nimitz, commander of the Pacific Fleet, based his Pacific strategy on the success of amphibious assaults, though he knew none of these victories would come easy. Never before had so many troops been moved across so many thousands of miles of ocean to fight on hostile beaches. The war in the Pacific would eventually cost more than 100,000 American lives, about double the number lost in the Vietnam War. The Pacific saw more maritime battles and more sunken ships in World War II than in all other modern naval campaigns combined.

In July 1943, Sears began preparing oceanographic chapters in a series of Joint Army Navy Intelligence Studies (JANIS) reports to assist in war planning at the strategic level. These reports would describe the geographic, physical, demographic and socioeconomic characteristics of a proposed military target—every detail that could affect a combat operation by land or sea. Sears had been selected to oversee the oceanography chapters of the reports. Because the Joint Chiefs would be using the studies to make pivotal decisions about every phase of the war, this classified research would take priority over everything else the Oceanographic Unit was doing.

It would take enormous effort to amass the data needed to cover all 33 oceanographic topics needed for a single region, much less to analyze it and translate it into lay terms that war planners could comprehend. Sears knew the added workload coupled with tight deadlines would overload her small team, but if the reports met their objectives, the Navy might avoid numerous hazards at sea, saving countless lives.

The members of Sears’ team fell into their natural roles in preparing the reports. Grier would comb the libraries and agencies around Washington, D.C. and anywhere else that held the best oceanographic data. Chace took the lead on charts and graphics. Henry, who had marked up many a graduate student’s thesis at the University of Washington, served as editor, compiling the sections while reviewing them for errors of any kind. Sears attended top-level meetings for briefings on upcoming military targets, helped analyze the stacks of data Grier brought back and translated the complicated scientific concepts into written text accessible to lay readers.

Oceanographic intelligence was especially crucial for the Pacific campaign. Amphibious operations were an orchestra of moving parts, each essential to the execution of the whole—and each presenting an opportunity for catastrophe. Even with the best planning, the missions faced inevitable hazards: hostile fire, reefs, swirling currents, rough surf zones and underwater obstacles. In retrospect, it’s painfully clear that the planning of the attack on Tarawa would have substantially benefited by the kind of in-depth JANIS report that Sears and her co-workers were beginning to produce. But by the time the JANIS program was up and running in the summer of 1943, only a few short months remained before this major amphibious assault would begin. Further, the oceanographers were subject to a Military Intelligence Services schedule that didn’t prioritize the Pacific campaign, and the Joint Chiefs had the oceanographers analyze Bulgaria as the subject of their first JANIS report.

on book cover showing the ocean near Japan
The oceanography chapter in this JANIS report prepared by Sears and her co-workers was one of 20 highly detailed intelligence publications they delivered to the Joint Chiefs. Courtesy of Wendy Nies

Lacking a comprehensive oceanographic analysis, the Marines were forced to rely on spotty oceanographic intelligence at Tarawa. Tidal estimates, mere guesses made on the basis of fallible memory and hearsay, proved ruinously inaccurate and left landing boats stuck on the island’s reef. The Marines had no choice but to bail out of their vessels and wade to shore through enemy fire.

That December, just a few weeks after the battle, the Senate Naval Affairs Committee asked Lt. Gen. Alexander A. Vandegrift, who would become commandant of the Marine Corps the following month, to answer questions about the heavy casualties at the Battle of Tarawa, up to that point the bloodiest fight in Marine Corps history. Following this grilling and the media scrutiny it prompted, and having read an avalanche of letters from grieving mothers of Marines lost in the battle, Nimitz re-examined his strategy. Even if the Navy could be relatively confident of victory from here on out, American lives were at stake. He had to figure out something to give amphibious forces a reliable edge through the remainder of the war.

For her part, Sears must have thrown up her hands in disgust when news of the debacle at Tarawa reached her. In planning those exhaustive JANIS reports filled with tables, charts, diagrams and advisories, her team had specifically noted concerns about “low water, lower at neaps than at springs.” The possibility of a prolonged neap tide like the one that had tripped up the landing boats at Tarawa was right there in black and white. Had the oceanographers been consulted ahead of the landing, no doubt Sears’ team would have issued clear warnings about the potential danger. Sears also would have included a detailed description of the coral reefs ringing Tarawa and noted how the combination of an obstructing reef and a dangerously low tide portended disaster.

Tarawa shook up the priorities for the team’s JANIS studies. Just two weeks later, urgent planning meetings for targets in the Philippines began. Soon, Sears’ team was assigned JANIS reports for the Marianas, the Carolines and the Palaus. Sears understood the importance of her mission. While she had no direct say in how the war would be fought, she could gather the very best oceanographic intelligence and get it into the right hands. She felt she owed it to the men who had lost their lives at Tarawa, the ones she never even got a chance to save.

Because they were prepared so far in advance, the JANIS reports couldn’t cover every contingency, so the Hydro team often had to answer questions on the fly. According to Sears, these urgent requests, a k a “quickies,” often followed meetings between U.S. President Franklin Delano Roosevelt and British Prime Minister Winston Churchill where the two were drawing up new war plans. When these quickies started rolling in, Sears would work all night if necessary to attend to each knotty query. On one occasion, she recalled, an aide to the Joint Chiefs showed up in her office late one night with a request for tide tables for a target in the Pacific so secret that only Sears could be trusted to make the calculations. Staving off exhaustion, Sears pulled tide tables for the nearest locations and extrapolated new ones for the secret location, all on her own. Bleary-eyed, she worked until morning with no one to check her top-secret arithmetic, all the time worrying that she would make an error. No one reported that she ever did.

Comprehensive studies of further Pacific targets were fast-tracked in the coming months, and Sears’ input proved invaluable. At the Battle of Okinawa, for example, she advised operations planners on their choice of landing beaches. Naval commanders favored landing on the western beaches of Hagushi because they offered 9,000 continuous yards of flat sand—but they also knew these same beaches were susceptible to strong gales. When planners consulted Sears, she performed a last-minute analysis and concluded that the waves at Hagushi would likely be calm. At dawn on April 1, 1945, the largest convoy of Marines and soldiers launched to date in the Pacific sailed toward Okinawa, and, as Sears predicted, there was scarcely a ripple in the sea. Less than three months later, the Allies had taken Okinawa and were establishing staging areas to prepare a possible invasion of the remaining Japanese islands. Sears’ timely, exhaustive insights, whether excerpted from her team’s reports or offered on demand in the middle of the night, helped guide the remainder of the Pacific campaign, while the bathythermograph, developed in no small part by her colleagues at Woods Hole, would provide Sears—and naval commanders in both the Atlantic and Pacific—crucial intel about the depth at which enemy subs would be most perceptible to sonar. The Joint Chiefs issued a new and accelerated priority list for the JANIS program. The Oceanographic Unit became busier than ever, at times working on three comprehensive reports at a time under tight deadlines while simultaneously responding to various urgent requests. The team would eventually issue 20 dense reports covering targets from the Black Sea to the East China Sea.

Sears' oceanographic experience helped the war efforts in other ways. Ahead of World War II, the U.S. Navy had been concerned about German U-boats, which had been so successful during World War I that they nearly paralyzed British lines of communications—not to mention interrupting supply lines for food and medicine. In response, the Royal Navy had organized convoys to protect merchant ships, narrowly saving the country in the Great War.

The U.S. Navy suspected the new generation of U-boats would be more precise and deadlier than ever, and with good cause: U-boat commanders had been refining their tactics, adding night surface attacks to their repertoire, as well as the use of wolf packs—groups of submarines working together to extend a search area and maximize strikes.

The Navy had asked Hydro whether there were worldwide charts that recorded the temperature of ocean water at varying depths at different times of the year. This data would help pinpoint thermoclines, the ocean layers with the greatest temperature differential, where a sudden change in temperature allows the water itself to bend sound waves, distorting sonar. Identifying thermoclines would help U.S. ships determine where enemy subs were most likely to be lurking. Unfortunately, that data didn’t exist. But WHOI scientists saw a way for the Navy to gather it: the bathythermograph.

a man holding a temperature measuring device off the side of a boat
Above, a researcher with a bathythermograph, which measures ocean temperature at varying depths. The data, right, helped Allied subs hide from sonar. © Woods Hole Oceanographic Institution; chart: National Archives

The perfection of the bathythermograph as an anti-submarine warfare tool had been a high priority at WHOI for years before the war. Once war broke out, Iselin advocated equipping as many ships as possible with the tool—not just naval vessels but also Coast Guard and merchant ships. Eventually, even submarines were equipped with a modified bathythermograph, which they could use to help locate thermoclines in real time, maximizing the efficacy of their sonar in hiding from the enemy.

Throughout the war, Sears collected and centralized bathythermograph data from WHOI and Scripps. While several scientists worked with her to analyze the data, it was Sears’ job to collect the information, ensure its accuracy and disseminate it to the submarine fleet. She became proficient at analyzing undersea conditions while compiling publications such as the Navy’s Submarine Supplements to the Sailing Directions, which outlined hydrographic conditions that could affect submarine operations such as sonar performance and diving maneuvers. “Sub-surface temperature gradients in the open sea are the chief factors in determining the paths of sound rays and thus delimit the effectiveness of underwater sound-ranging equipment,” she wrote. “Familiarity with these conditions will therefore aid a submarine to avoid detection by diving to the optimum depth, and it will conversely inform surface vessels concerning ranges and depths at which enemy submarines are likely to be encountered.”

a group of woman naval officers in an office setting
WAVES assigned to the Maritime Security Division assisted Sears’ team and responded to other military requests for oceanographic data. U.S. NAVY

Sears often included observations from U.S. submarine patrols in Submarine Supplements: In one instance, she recorded, “Sound conditions in general were poor....The targets were not heard until the range was 100 yards. The large freighter we tracked was never heard by sound.”

These were the sort of play-by-play descriptions that submarine commanders were thrilled to receive. Sears’ reports offered a clearer idea than ever before of what to expect from the oceans. The Navy could not have obtained and centralized this information in any other way. Sears’ advisories, and the on-demand expertise that she provided at any time of day or night, helped the Navy win the Pacific.

Even though so much of Sears’ work was confidential, she was well regarded in the Navy—and word of her achievements began to trickle out.

“Please thank Miss Sears for me in regard to the studies put out by her unit,” wrote Lt. Charles L. Burwell of the Atlantic Fleet to Lt. Cmdr. B.E. Dodson, Sears’ immediate supervisor. Burwell, a highly respected naval intelligence officer, would go on to brief commanders on weather and surf conditions ahead of the landing at Normandy; later, at Okinawa, he would incorporate many of the Oceanographic Unit’s findings into operational plans.

After the war, the Oceanographic Unit expanded into a permanent Oceanographic Division, with Sears as the first officer-in-charge. The Navy would never have to go to war again without crucial oceanographic intelligence; Sears’ efforts had made the Navy a more capable fighting force. She retired from active service on June 4, 1946, and, still prohibited from American research vessels, headed to Denmark for a year to spend time on the Norwegian research vessel Gunnar Knudsen. Upon her return to the States, she rejoined Woods Hole in 1947 as a planktonologist and was promoted to senior scientist in 1963.

a group photo at the entrance of a brick building.
Sears (center,middle row) in 1950 with Woods Hole colleagues, including Henry Bryant Bigelow (center, first row, hat on lap) and Columbus Iselin (first row, third from left). © Woods Hole Oceanographic Institution

Sears continued her own research but also took on the role of organizer for the emerging field of modern oceanography. In 1953, Sears became a founding co-editor of Deep Sea Research, which came to be recognized as the premier journal of oceanography. She also coordinated the first International Oceanographic Congress in New York in 1959. In taking on these responsibilities, Sears helped to organize a loosely connected research community into a cohesive, recognized scientific field. A self-proclaimed obsessive bibliographer who kept those extensive index card files, Sears saw her vast collection published by G.K. Hall & Co. in 1975 as a 15-volume oceanographic index that served as a testament to her unparalleled knowledge of the sea.

Two decades after the war, Iselin wrote of Sears: “She has done as much for the advancement of oceanography as anyone I know.”

After retiring in 1970, Sears was a familiar sight around the village of Woods Hole, riding her bicycle, walking her dog and swimming in Vineyard Sound. When she died at 92 in 1997, there was an outpouring of sentiment from the oceanographic world, and visitors paid her honor at a grave marked with a simple headstone in the village cemetery.

a naval ship
The United States Naval Ship Mary Sears had its maiden voyage on October 19, 2000. © Woods Hole Oceanographic Institution

Sears’ half-sister, Leila Sears, served as a WAVE in the Navy’s code decryption department in World War II. Leila remembered one day during the war when she delivered a stack of decrypted dispatches to Admiral Nimitz’s office in the Pentagon for review and signature. While going through the reports, Nimitz noticed the name tag “SEARS” on the young courier’s uniform and asked if she was related to Lt. Mary Sears. When Leila told Nimitz that Mary was indeed her older sister, he rose from his chair, took both her hands in his and said, “Someday the country will learn how much it owes to your sister Mary.”

That day came on October 19, 2000, when Leila gathered with Mary’s family and friends at Halter Marine shipyard in Pascagoula, Mississippi. They were there to christen an oceanographic survey ship, the USNS Mary Sears.

Adapted from Lethal Tides: Mary Sears and the Marine Scientists Who Helped Win World War II, by Catherine Musemeche. Copyright © 2022. Used by permission of William Morrow, an imprint of HarperCollins Publishers.

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