“Lethal Tides – Mary Sears and the Marine Scientists Who Helped Win World War II” by Catherine Musemeche is a thorough biography of the sort of person that is easy to overlook. Sears was an unassuming marine biologist who wound up heading the Oceanographic Department of the Naval Hydrographic Office during the War. She was the one of the Women Men Don’t See, as in James Tiptree’s memorable story, but her work, and that of the researchers she directed, saved a lot of lives.

She was born in well-to-do circumstances in Massachusetts, but lost her mother early to polio. Her step-mother was an alumna of Radcliffe, so she went there and eventually got a PhD in zoology in 1933. She worked at the great Museum of Comparative Zoology at Harvard under Charles Bigelow, a founder of the Woods Hole Oceanographic Institute (WHOI). It and Scripps are the leading ocean research centers right down to today. They wouldn’t let her on the research cruises, though, because dames is trouble. She finally got out to sea in 1941, studying plankton in the Pacific off Peru, which are crucial to the seabirds on whose guano Peru depended for exports. She didn’t actually hear about Pearl Harbor until she got back.

WHOI had immediately mobilized for the war. Most of their people enlisted, and the remainder started working on things like keeping ship hulls from getting fouled, and exploiting density layers in the ocean to let submarines hide from sonar.

The Navy knew that it was going to have fight the Japanese across the Pacific, and knew that it was going to need to know as much as it could about all the islands on the way. So they went to WHOI and asked for oceanographers to do all this charting. Almost everyone was gone! So the head of WHOI said, how about Mary?

They were skeptical. She was older, 37, and had already tried to enlist and failed a medical exam. Still, they didn’t have much choice, so they made her a lieutenant in the WAVES (Women Accepted for Volunteer Emergency Service) and set her up in the Oceanographic Division in 1943.

Musemeche notes an odd thing about the WAVES – their uniforms were the best outfits most of them had ever worn. They were designed by a major New York couturier, Main Rousseau Bocher, and were made of stylish and durable wool. All of these women from the provinces finally got to wear clothing made to national levels.

Anyway, the Division was a great match to Sears’ skills. She knew people from universities all over the country and got them to join. They quickly started assembling the thousands of charts needed.

The need for her skills was seen immediately. In November 1943, the tiny atoll of Tarawa, about halfway between Hawaii and Australia, was attacked by a force of 18,000 Marines. They came in on amphibious craft called Higgins Boats that needed about four feet of water. Unfortunately, it was a neap tide and there was only 3 feet above the outer coral reef. The boats were stranded there under withering Japanese fire. About a thousand Americans were killed in the three-day battle, a lot of them due to this failure of mapping and oceanographic knowledge.

Sears and her team were NOT involved – they were working at that time on the marine mapping of Bulgaria. No one knew why, but that was their orders. Yep, it takes a while to get agencies straightened out. They were immediately re-directed to the Pacific. The next goal was the Marianas Islands (Saipan, Tinian, and Guam), but they had never been charted. One of her researchers, Mary Grier, found that Japanese marine biological expeditions had explored them in the 1920s. The Emperor happened to be fond of marine life. It was all published in Japanese, and was in the bowels of the Library of Congress, like everything else written by humanity. They used that and maps from the voyage of the HMS Challenger in 1876.

The key data for amphibious landings are the tides, as seen at Tarawa. These are normally calculated by taking measurements over a couple of months, and applying a Fourier transform to find their frequency components. This was figured out by George Darwin, son of Charles. Sears didn’t have that data, but could make estimates based on topography and astronomy. She came up with the components and their phases and then ran them on Old Brass Brains (more boringly known as Tide-Predicting Machine No. 2), a unique analog computer in Washington DC that used slotted crank yokes to sum up all the frequencies to get the time-domain values of the rise and fall levels. It was a remarkable mechanism that ran from 1910 until 1965, when it was finally displaced by digital. It’s still on display at NOAA.

The Hydro Office used all this to create the Joint Army Navy Intelligence Studies (JANIS), huge documents that were distributed all across the military and described everything that they might come across. The version for the Marianas campaign in June 1944 was still not quite complete. When the Marines landed on Saipan, the waves were much too steep and choppy to easily get across the reef. They were blasted by Japanese fire again. Tinian and Guam went better over the next two months, but the Japanese still fought with extreme tenacitiy, prompted by propaganda about what the barbarous whites would do to them.

The invasion of Palau in November 1944 was also tough, but by Luzon (Jan 1945) and Okinawa (April 1945), the Hydro Office had hit its stride. The conquests themselves were bloody, but they had the landings down. They were then busy charting everything they could about Japan itself. The plan was to invade its southern island of Kyushu in November 1945, and take Tokyo in March 1946. Even though FDR died in April, and the war in Europe ended in May, the Office was still going all out. Then came Hiroshima and Nagasaki in August. Emperor Hirohito gave the surrender speech in his first ever radio broadcast, and set a world record for under-statement with “the war situation has developed not necessarily to Japan’s advantage.”

Everyone was overjoyed, of course, but the Office’s work turned out to be crucial even after the fighting stopped. About 36,000 Allied POWs were being kept in 140 camps around the Far East. The main and sometimes only information on how to get to these camps was in the Office’s JANIS reports. They were so useful that it was recommended that the series be kept going, since the US was clearly now going to be the world’s policeman. The CIA took them over in 1947, and produces versions to this day.

Sears ran the Hydro Office until June 1946, steadily expanding its capabilities. It became its own division of the Navy, and then a separate Office. By 1976 it out-grew DC office space and moved to southern Mississippi, where it’s called NAVOCEANO. Sears went back to Woods Hole as a senior scientist, and founded and edited two major journals: Deep Sea Research and Progress in Oceanography. She became a trustee of the Marine Biological Laboratory, and the Clerk of the WHOI Corporation. She retired from the Navy in 1963 with the rank of commander, and from WHOI in 1970. She was often seen around Woods Hole, riding her bike, walking her dog, and sailing her boat, the Piquero, named for a kind of guano bird that she had studied way back when in Peru.

She died in 1997 at the age of 92. In 2000, the Navy christened their oceanographic survey ship the USNS Mary Sears. It’s 5000 long tons, 100 m long, and is still in service. It was christened by her sister Ariel. There are about 2500 personnel today in the US Naval Meteorology and Oceanographic Command. An office that started as just her and three others with oceanographic backgrounds has become a significant operation!

Most people are bemused by scientists. They find it hard to imagine devoting one’s life to something like the study of plankton and currents. For Sears, her work really was her main fulfillment – she had siblings and nieces and nephews, but no family of her own. She was in a field that in her day didn’t particularly respect women. Her Hydro Office work actually did earn her great respect, and that carried over into her later career at WHOI. Yet it was the work itself that sustained her.

It’s people like this who shine in times of national crisis like the War. No one cared about currents and tides in distant oceans until they became literally a matter of life and death. Then even short, shy people have a role to play. They get overlooked in the bustle of a mercantile nation, but they know how the real world actually works, and that’s always going to matter at some point.