Home Business and Labor Amazing Grace Hopper, COBOL Inventor and Slayer of Dragons, Gremlins and Bugs

Amazing Grace Hopper, COBOL Inventor and Slayer of Dragons, Gremlins and Bugs

But she never pulled a moth out of a computer


In 1946, the U.S. Navy considered Grace Hopper too old to be an officer.  Thirty-seven years later, President Ronald Reagan promoted her to rear admiral because of her pioneering work in computers.Photo courtesy National Archives.

In 1986, she told David Letterman about meeting the president.

When I met him I tiptoed up to him and got up on my toes and said, ‘Sir, may I tell you something?’ And he looked at me funny as all get out, as if I was going to threaten something, and I said, “I’m older than you are.” He got out a laugh you could hear across the country.

But even in her 70s, Grace Hopper had a better grasp of how computers would change our lives than most younger people did.

She ushered in the computer revolution starting in World War II, developing crucial languages and programs and laying the foundation for the computer programming profession.

Ironically, she gets credit for something she did not do: Pull a moth out of an early computer and coin the expression “computer bug.”

Becoming Grace Hopper

Photo courtesy National Archives.

She was born Grace Brewster Murray on Dec. 9, 1906, in New York City, the great-granddaughter of a Navy rear admiral and the daughter of a prosperous businessman and his wife. She grew up in privilege on the Upper West Side of New York, with private schools and summers spent on Lake Wentworth in Wolfeboro, N.H.

Her parents sent her to Vassar College, where a scientist named Maria Mitchell had been the first person appointed to the faculty. Grace graduated Phi Beta Kappa in 1928 with a bachelor’s degree in mathematics. In 1930, she earned a master’s in mathematics from Yale, the first woman to do so. Four years later, she got her Ph.D. in mathematics from Yale.

Grace Hopper Meets Mark I

She married another academic, Vincent Hopper, and taught math at Vassar. By 1940, bored with the classroom, she took a sabbatical to study at NYU with Richard Courant, an applied mathematician who had escaped Nazi Germany. They worked on partial differential equations, the mathematical foundation for aerodynamics, hydrodynamics, electrical engineering and quantum mechanics.

When the United States entered World War II, Grace Hopper’s husband, brother, cousins and many friends joined the military. She wanted to contribute, too. She wanted something more than her job, which didn’t challenge her, and her marriage, which had failed.

Grace divorced her husband, left her tenure-track professorship at Vassar and joined the Naval Reserves in the WAVES (Women Accepted for Volunteer Emergency Service). She had to get waivers because of her size (105 lbs.) and, at 38, two years too old. She graduated first in her class at boot camp – the U.S. Naval Reserve Midshipmen’s School at Smith College in Northampton, Mass.

grace hopper mark iiWhile she was in Northampton, a huge machine called the Automatic Sequence Controlled Calculator had been shipped to Harvard from an IBM laboratory in Endicott, N.Y. Howard Aiken, now a lieutenant commander in the Navy, had come up with the idea for a mechanical arithmetic machine that could speed the hand calculations required for his thesis on the propagation of radio waves.

IBM had spent eight years and $250,000 for the thing, which measured 51 feet long, 8 feet wide and 8 feet deep. Today, its computing power could be stored in a tiny corner of a microchip. Harvard operated it under a contract with the U.S. Navy Bureau of Ships and named it the Mark I — the first computer in the U.S.

Harvard Hotbed

grace hopper labBy 1944, it was becoming clear the war could be won by technical and scientific breakthroughs.  Calculations were needed to create implosion devices for the atomic bomb. Engineering problems needed to be solved for the new aircraft and ship hulls being designed. Missiles were coming into use, and their trajectories needed to be calculated. New magnetic mines were set off by metal ships; the navy had to know how far the explosion would extend so they could figure out how close to each other they should be placed.

Until then, mathematical problems had been solved by teams of human beings. But the new machine was so much more powerful than anything else available then that it was used for many of the scientific developments of World War II, concluded Kathleen Williams in Grace Hopper: Admiral of the Cyber Sea.

On July 2, 1944, Lt. (j.g.) Grace Hopper was taken under armed guard to Harvard’s Cruft Physics Laboratory. “Where have you been?” asked her fearsome new boss, Howard Aiken. He barked at her to solve a mathematics equation on the machine she had never seen before.

She would spend the rest of the war with a small staff that worked around the clock under intense pressure. Sometimes she slept on her desk. Sometimes she didn’t sleep.

The projects were so secret, wrote Wheeler, “even the coders usually identified them only by letters of the alphabet.”

Hopper called what came to be the Harvard Computation Lab as “a hotbed of ideas and concepts and dreams.”


The Mark I was noisy and often balked because something went wrong. Wire brushes inside the machine sometimes frayed and sparked; the researchers found out which ones were stopping the machine by borrowing Grace Hopper’s mirror from her Navy-issue handbag. She developed a nomenclature for the problems that plagued the machine:

A “dragon” chewed holes in the paper tape that fed instructions to the Mark I, and a set of “gremlins” picked up the small dots of paper that had been punched out of the tape and replaced them. She drew cartoons of imaginary bugs: a table worm, the NRL bug, the kitchie boo boo bug. She was irreverent to the point of insubordination, wrote Kurt Beyer in Grace Hopper and the Invention of the Information Age.

Aiken one day ordered her to write a manual for the Mark I. She replied she’d never written a book before. “You’re in the navy now,” he said. She came up with a 561-page manual for the machine.

When Aiken heard the machine go silent, he demanded to know why. The staff learned to assuage him by saying they were “debugging.”

End of the War and a Moth


Grace Hopper in 1960

When the war ended, Grace Hopper wanted to transfer to the regular Navy. But at 40 she was two years too old. She stayed at Harvard with Aiken and worked as a research fellow under contract with the Navy to develop more powerful computers: the Mark II and Mark III. The Mark II was five times faster than the Mark I; the Mark III was 50 times faster than the Mark II.

In the summer of 1947, the Mark II spit out incorrect results. The programmers discovered the cause of the malfunction: a moth. It was taken out of the computer with tweezers and taped into a page of the logbook. Someone wrote, “First actual bug found.”

Grace Hopper often gets credit for plucking the moth from the computer and coining the expression “computer bug.” Actually, usage of the term dates to Thomas Edison. But Grace Hopper popularized the term as she continued to develop computers.

In the late ‘40s, even IBM didn’t think there’d be much business use for computers. Grace Hopper did the unthinkable in 1949 and rejected a tenured professorship at Vassar to work on computers in the private sector.

“Life is too short to keep doing the same thing over and over and over again,” she once said.


Back then, even IBM didn’t see much business use for computers.

Grace Hopper invented new programs and languages and technologies that allow computers to program themselves. She invented the computer language COBOL (COmmon Business Oriented Language), once the most common language, just as its name says.

In 1967 she went to work as the director of the Navy Programming Languages Group in the Navy’s Office of Information Systems Planning. The Navy promoted her to captain in 1973. She urged the Defense Department to replace large mainframe-based computer systems with networks of small machines. She understand that someday people would be communicating desk-to-desk with their computers.


Grace Hopper retired from the Naval Reserve in 1966, then returned twice. All told, she spent 43.5 years in the Navy.

In 1983, the television program 60 Minutes interviewed her, calling her a member of the small band of brothers and sisters who ushered in the computer age. U.S. Rep. Phil Crane, an Illinois Republican, saw the show and introduced a bill to have her promoted to commodore. Ultimately she won a promotion to rear admiral, by presidential order.

Grace Hopper died Jan. 1, 1992. Today, 23 years after her death, the woman nicknamed “Amazing Grace” is the most numerically popular computer pioneer on the Web.

To see snippets from the Grace Hopper 60 Minutes interview, click here. To see the 1986 grace Hopper interview on David Letterman, click here.   Photos courtesy National Archives. This story was updated in 2023.

Image: Grace Hopper at the Univac By Unknown (Smithsonian Institution) – Flickr: Grace Hopper and UNIVAC, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=19763543.


Robert Nolin December 10, 2015 - 10:56 am

Grace Hopper invented the computer language COBOL (COmmon Business Oriented Language), which was once the most common language, just as its name says. I was a COBOL programmer for 15 years, which is why I was disappointed to see no mention of COBOL. It looked like this:

Perform 010-write comment thru 010-exit.

English-like, right down to the required (and easy to miss) periods.

Robert Nolin December 10, 2015 - 11:08 am

Oops, just noticed a compiler error, missing hyphen: should’ve coded it as
Perform 010-write-comment thru 010-exit.

At the millenium, the Y2K problem involved searching the estimated 300 billion lines of COBOL for dates that lacked the century portion (1959 was stored as 59, as in 01/01/59).

Erkki Hakalainen October 31, 2017 - 1:54 am

51 feet long, 8 feet long?

Margaret Hamilton, the Woman Who Put the Man on the Moon - New England Historical Society July 20, 2019 - 8:00 am

[…] about another pioneering computer scientist, Grace Hopper. This story was updated in […]

Williamina Fleming, From Scottish Maid to Harvard Astronomer - New England Historical Society December 5, 2019 - 10:10 am

[…] The observatory employed computers, people who did mathematical calculations by hand. Pickering's male computers supposedly disappointed him with inferior work. Hence the apocryphal exclamation about his Scotch maid. […]

Comments are closed.

Subscribe To Our Newsletter

Join our mailing list to receive the latest artciles from the New England Historical Society

Thanks for Signing Up!

Subscribe To Our Newsletter

Join Now and Get The Latest Articles. 

It's Free!

You have Successfully Subscribed!