At 4:17 a.m. on May 25th, 1942, the ocean was still dark outside Honolulu, but inside the Fleet Radio Unit Pacific headquarters, the war was fully awake.

The room had no windows. No clocks anyone looked at. Just rows of battered desks under humming fluorescent lights. The air smelled of hot dust, carbon paper, and cigarettes burned down to the filter. Teletype machines chattered endlessly, spitting out new strips of five-digit numbers—33,000 possible code groups, rearranged and re-encrypted every day into a language no one could read.

Men in khaki shirts bent over them: mathematicians who used to teach in universities, engineers who once designed bridges, now staring at columns of digits until their eyes burned. On the wall, a huge map of the Pacific sagged under red strings and pushpins, a web of possible routes, probable convoys, suspected ambushes. One thin red thread ran straight to a tiny speck labeled MIDWAY.

They suspected the Japanese were coming for it. But suspicion couldn’t move carriers. Only proof could.

In a corner of the room, at a desk no one paid much attention to, sat a 24-year-old woman named Margaret Howard.

Her Navy file said clerical assistant. She lived in a converted dorm up near Makiki Heights, walked to the base before dawn, passed beneath the gate while the guards barely glanced up. Women came and went all day—secretaries, typists, file clerks. The war needed paper pushed as badly as it needed shells fired.

Margaret’s job looked simple from a distance. She took freshly intercepted Japanese naval traffic—long sheets dense with five-digit groups—and retyped them cleanly on an old Underwood standard. No smudges, no mis-spaced digits. A single error could send the codebreakers down the wrong path, and they were already lost enough.

She wasn’t supposed to interpret. She wasn’t supposed to think.

But repetition has a way of teaching you its own lessons.

After her first few weeks, she began to feel the numbers. Her pre-war job as a bookkeeper in Chicago had trained her eye: the way certain columns looked wrong, the way duplicate entries echoed on ledgers. Now, in Honolulu, she started seeing familiar clusters of digits the way a musician hears a returning phrase.

Sometimes it was exact: a group like 73941 appearing again and again, days apart. Sometimes it was almost the same, different by a single digit. She started putting tiny pencil dots beside the familiar ones as she typed, just to keep herself honest.

Her typewriter ribbon was old, overused. After hours of work, faint “ghost” impressions of previous lines shadowed the fresh ink. If she lifted the ribbon against the light, she could see two layers of numbers faintly superimposed, like an echo.

One afternoon, she changed the ribbon and—on a whim—left the old one on her desk instead of throwing it away.

When her shift was over and the room was mostly empty, she unspooled it, curious.

Under the white glare of the lamps, she saw it clearly: the same five-digit group imprinted almost on top of itself, separated only by the space from one sheet to the next. Not once. Many times. Every twelve lines or so, a little darker, where the keys had struck the same place twice.

It looked like music. A rhythm someone else hadn’t meant her to hear.

Margaret took the marked pages and the ribbon to a young communications officer she trusted, Lieutenant Tom Davis. He had the hungry look of someone who still believed the code could be broken.

“It’s probably nothing,” she said, suddenly shy as she showed him the pages with her neat dots. “But these groups… they repeat. The same ones. And when they do, they leave a shadow on the ribbon.”

He looked. Really looked. Counted the lines between the repeats. Checked the message times.

“Twelve-line interval,” he muttered. “Tokyo to Truk. Same format. Same length.”

He realized before she did what that meant.

If the Japanese operators were reusing an additive key—if, through tiredness or haste, a radio man had used the same line of his random-number table twice—then two messages encrypted with the same key could be subtracted from one another. The masking numbers would cancel out. Underneath, for the first time, the shape of the original code groups would show through.

It was a tiny imperfection. But in a system built on the illusion of perfect randomness, one human slip was all it took.

Davis brought the ribbon to Commander Joseph Rochefort.

Rochefort, the rumpled, chain-smoking head of the Honolulu unit, had been living off black coffee and stubbornness for six straight months. He’d watched every promising lead evaporate under the weight of JN-25B’s mathematics.

He examined the ribbon, then the marked intercepts. For a long moment, he didn’t say anything.

Then he laughed. A harsh, startled sound.

“We’ve been wandering in a dark room,” he said softly. “Miss Howard, you may have just shown us where the door is.”

He gave one order that night that changed everything:

“No one throws away another ribbon. Ever.”

From that moment, Margaret’s routine changed. She wasn’t just retyping. She was feeding a new kind of machine.

The analysts built what they called the additive table: a growing catalog of repeated number strings where the Japanese operators had reused their key. With each pair of messages that shared a pattern, they could peel away a little of the random “mask” and expose fixed code groups underneath—words and phrases that appeared again and again in naval traffic.

Carrier division.
Refuel.
Commence air attack.

It was slow, painful work. Sheets of tracing paper layered over grids of digits. Columns of subtraction done by hand. The room buzzed with the scratch of pencils and the staccato of typewriters. Margaret sat beside Davis, typing out recovered code groups as fast as he and the others could derive them.

Day and night stopped making sense. The blackout curtains stayed closed; the only time they knew it was morning was when coffee arrived in the thermos.

They weren’t breaking today’s messages yet. JN-25 still changed too often. But they were reconstructing big chunks of the codebook—those 33,000 five-digit groups that corresponded to Japanese words and phrases.

That was the first half of the battle.

The second half—the additive tables—would follow.

In late May, something new appeared in the growing library of deciphered words: AF.

They’d seen “AF” before in raw traffic and suspected it was a place code. Now it appeared in clear context:

“AF will soon run short of water.”

Midway Island was low on fresh-water storage and often had shortages. Rochefort suspected AF meant Midway. But suspicions don’t move fleets. Admiral Nimitz wanted proof.

Rochefort came up with a test as simple and audacious as Margaret’s ribbon.

He had the Midway garrison send an uncoded radio message: “Fresh water plant out of action. Short of water.”

They knew the Japanese were listening.

Two days later, Tokyo sent encrypted traffic. When Rochefort’s team worked on the new messages, the phrase surfaced:

“AF reports water shortage.”

AF was Midway.

The target was confirmed.

Margaret was in the room when they pinned that message to the board. Men who hadn’t slept in two days hugged each other. Some swore. Some cried.

Admiral Nimitz got the summary: Enemy striking force—approx. four carriers—will attack Midway from the northwest at dawn, 4 June.

He believed it.

The orders went out. USS Enterprise, Hornet, and the battered Yorktown turned toward a point in empty ocean that, thanks to numbers on a page and a torn ribbon in a drawer, wouldn’t be empty for long.

On June 4th, 1942, Margaret was at her typewriter in Honolulu when the first real-time message from Midway came through:

“Many planes heading your way, bearing 320, distance 150 miles.”

The Japanese were coming, exactly on time, exactly from the direction the codebooks said they would.

All day, the code room mirrored the chaos at sea—but in numbers.

Messages from scout planes:
“Enemy carriers sighted.”

From Midway’s bombers:
“Hit on carrier.”
“Lost contact.”

From the American task force:
“Under attack.”
“Yorktown hit.”

Margaret typed them all, feeding updated situation reports to Nimitz’s staff. She saw the rough story form before anyone else would:

Three American squadrons found the Japanese carriers while their decks were full of refueling and rearming aircraft. Bombs dropped. Fuel lines ignited. In less than five minutes, Akagi, Kaga, and Sōryū were mortally hit. Hours later, Hiryū fell too.

Four carriers gone.
Fed by the same code system that had seemed unbreakable six months before.

Back in Honolulu, no one cheered when the confirmation came in:

“Enemy carrier force destroyed.”

They just sat very still, letting the tide of it wash over them.

Rochefort took off his glasses and rubbed his eyes. “They walked right into it,” he said.

Lieutenant Davis nudged Margaret. “Your ribbon did that.”

She shook her head. “No. They did. The men on the ships.”

Privately though, she allowed herself one small thought:

We were not blind.

The next day, the celebrations began—everywhere except the code room.

Newsreels called Midway a miracle of American courage and luck. The official story credited daring pilots and aggressive admirals. Intelligence got a vague nod: “improved scouting.”

The existence of the Honolulu codebreakers, the patchwork additive tables, and the woman who had first spotted the crack in JN-25’s armor were all stamped SECRET.

Rochefort gathered his people and told them bluntly:

“What we did stays here. You will tell no one, ever, how we knew. If anyone asks, tell them we guessed. Tell them we were lucky.”

They signed papers. Margaret tucked her notes into boxes marked for destruction. The torn ribbon—the piece of cloth that had helped expose a fleet—went into a safe as Evidence 14.

The war rolled on—Guadalcanal, the Solomons, Tarawa. Every time a new Japanese operation stirred, JN-25 no longer looked invincible. They had footholds now, known words, stable additives. The enemy’s numbers weren’t opaque anymore; they were a language the team could speak.

For the rest of the war, Margaret remained what her file said she was: clerical staff. She moved intercepts, typed decrypts, logged timestamps. When V-J Day came and church bells rang and ships in Pearl Harbor blew their whistles until they ran dry of steam, her last duty was filing the final JN-25 logs for archiving.

Then she went home.

In Chicago, Margaret found a job at an insurance firm. The tools were the same—typewriter, carbon paper, ledgers. The stakes were different. Premiums instead of carriers. Claims instead of convoys.

When people found out she’d been in the Navy in Hawaii, they smiled and said, “Were you a nurse?”

She said, “Something like that,” and changed the subject.

Once, in 1960, she read a magazine article about Midway. It described it as a “naval miracle” won by guts and good fortune. Intelligence, if mentioned at all, was a line or two about “radio scouting.”

She clipped the article, wrote in the margin, It wasn’t luck, and placed it in a box labeled 1942.

Next to it, she kept a small photograph of herself in uniform, taken outside the Honolulu building: a young woman with a neat bun and serious eyes behind round glasses. On the back she’d written, in careful script, FRUPAC—classified.

When she missed the old days, she would roll a typewriter carriage back and type strings of numbers:

27391 45062 99104 18273 …

Just to hear the rhythm again. Just to remind herself that once, for a brief time, she’d stared into that ocean of digits and found a ripple that mattered.

In the early 1980s, as JN-25 files were declassified, a naval historian traced a note in a 1942 memo: “Observation by female clerical staff led to discovery of additive repetition in JN25 traffic.”

No name, just a reference.

He dug through duty rosters for the Fleet Radio Unit Pacific. Among dozens of names, he found one: Howard, M.—clerical staff.

He found her in a modest flat overlooking Lake Michigan. She was in her sixties, hair silver, voice still precise.

“Mrs. Howard,” he said, “I think you helped win the Battle of Midway.”

She smiled politely. “I typed,” she said. “The men did the hard work.”

He asked to record an interview. She declined.

“It was a team,” she said. “And the ribbon’s gone.”

She died in 1989. Her obituary mentioned she’d been a Navy veteran and a secretary. Nothing about JN-25. Nothing about Midway.

Three years later, in the National Cryptologic Museum’s storage, archivists cataloguing old evidence envelopes pulled out a brittle strip of fabric labeled No. 14. Under magnification, they saw faint double impressions of five-digit groups, recurring every dozen lines. Exactly what the early decrypt notes described.

They logged it as: “Typewriter ribbon used in early JN-25 traffic analysis.”

It sits now in a climate-controlled drawer. Visitors walk by exhibits about Enigma and Navajo code talkers and never see it.

Just a strip of old cloth, stained with ink from 1942.

But in its faint shadows is a record of two kinds of imperfection:

A Japanese operator reusing a key he should have thrown away.
An American typist refusing to throw away a ribbon everyone else thought was spent.

Those two flaws, stacked on top of each other, opened a door in a wall of numbers and let the Pacific Fleet see an ambush coming.

We remember admirals and pilots. Their names are on ships and statues.

We rarely remember the people in windowless rooms who notice small, “unimportant” things and won’t let them go.

The war in the Pacific turned at Midway. Midway turned on intelligence. That intelligence turned—at least in part—on a pair of tired eyes and a torn ribbon.

Margaret Howard never got a medal. She never asked for one. Her contribution is a line in a file, a ghost on a strip of ink, a handful of pencil dots on old intercepts.

But if you follow the chain of cause and effect—if you trace it from burning carriers back to orders sent, back to encrypted messages, back to repeated keys, back to a piece of ribbon stretched between two hands in a fluorescent-lit room—you find her.

A young woman at 4:17 a.m. who decided a pattern was worth paying attention to.

Sometimes that’s all it takes to change the course of a war.