Grace Hopper: A Life in Five Chapters

Chapter 1 · Seven Alarm Clocks

A curious child and a Yale doctorate

1906 – 1943 · New York · Vassar · Yale

Grace Brewster Murray was born in New York on 9 December 1906. At seven she dismantled an alarm clock to find out how it worked, could not reassemble it, and worked through six more before her mother limited her to one. Her family encouraged the curiosity; her great-grandfather had been a rear admiral, and her father, who lost both legs to circulatory disease, insisted his daughters be educated to support themselves.

She went to Vassar in 1924, studied mathematics and physics, and graduated in 1928. At Yale she took a master's in 1930 and a doctorate in mathematics in 1934 — a rare achievement for a woman then, and one of a small number awarded in that period.

She returned to Vassar to teach, and her teaching was distinctive. She required her mathematics students to write, arguing that a mathematician who could not explain their work clearly had not finished the job. She also audited courses in other departments to find applications her students would care about.

After Pearl Harbor she tried to join the Navy. She was rejected twice: at thirty-six she was above the age limit, she was fifteen pounds under the minimum weight for her height, and her employer argued her mathematics teaching was essential war work. She obtained waivers, took leave from Vassar, and was sworn into the Navy Reserve in December 1943.

She graduated first in her class from midshipmen's school and was assigned to the Bureau of Ships Computation Project at Harvard.

Why this matters

Hopper's insistence that mathematicians must be able to explain themselves in words anticipates the work she is remembered for: making computers programmable in something closer to human language.

You have met the professor who joined the Navy. What would you ask her?

Ask Grace

• “Why did you take apart seven alarm clocks?”
• “Why did you make mathematics students write essays?”
• “What did you have to do to be allowed into the Navy?”
• “How unusual was a woman with a mathematics doctorate in 1934?”
• “Why did you want to serve rather than keep teaching?”

Chapter 2 · The Mark I

Fifty-one feet of relays, and a moth

1944 – 1949 · Harvard

The Harvard Mark I was a fifty-one-foot electromechanical calculator, driven by a rotating shaft, containing some 765,000 components and miles of wire. Hopper arrived in 1944, was shown the machine by Howard Aiken, and was told she would compute the coefficients for the interpolation of the arc tangent by the following Thursday. She had never seen a computer, and did not know what he meant.

She learned it, and then wrote the manual: 561 pages describing the machine's operation and the mathematics it could do. It was the first substantial book about programming a computer, and it taught a generation.

The machine's wartime work included calculations for the Manhattan Project, requested by John von Neumann, on the implosion problem.

In September 1947 the team working on the Mark II traced a fault to a moth caught in a relay. They removed it and taped it into the logbook with the note that this was the first actual case of a bug being found. The words bug and debugging were already engineering slang, so Hopper did not coin them; what she did was tell the story for the rest of her life, and it fixed the terms in computing. The logbook, moth still attached, is in the Smithsonian.

Her working principle from these years was that programmers should not waste effort repeating what a machine could do for them. She kept a notebook of routines that worked and copied them into new programs — the beginning of the idea of a subroutine library.

Why this matters

Hopper's Mark I manual was the first comprehensive book on programming a computer, written before the profession or the vocabulary existed.

You have the first machine. What would you ask her?

Ask Grace

• “What was it like to be handed a computer with no instructions?”
• “Why did you write a 561-page manual?”
• “Did you invent the word 'bug'?”
• “Why did you keep a notebook of reusable routines?”
• “What did the Mark I calculate during the war?”

Chapter 3 · The Compiler

Being told for three years that it could not be done

1949 – 1955 · Philadelphia

In 1949 Hopper left Harvard for the Eckert–Mauchly Computer Corporation, working on UNIVAC I, the first commercial computer in the United States.

Programming at the time meant writing machine instructions in numeric code, by hand, for a specific machine. It was slow and error-prone, and every program had to be rewritten from scratch for different hardware.

Hopper's idea was that the computer could do this work itself. If you wrote instructions in a more human-readable form, a program could translate them into machine code. In 1952 she produced the A-0 system, generally recognised as the first compiler — technically closer to what would now be called a linker or loader, but the principle is the same: the machine translating the programmer's notation into its own.

The resistance was substantial. She said repeatedly that she was told for about three years that it could not be done, on the grounds that computers only did arithmetic. Her response was to build it and demonstrate it.

She went further with FLOW-MATIC, completed around 1955, the first programming language to use English-like statements — commands such as COMPARE and TRANSFER rather than numeric codes. Her argument was practical: businesses would only adopt computers if their own staff, not only mathematicians, could write and read the programs.

She also made a broader point that has aged well: that the greatest obstacle to progress was not technical but the sentence 'we have always done it that way'. She kept a clock on her office wall that ran backwards, to demonstrate that things could be done differently and still work.

“The most damaging phrase in the language is: 'We've always done it this way.'”

— Grace Hopper, quoted in Computerworld, 1976

Why this matters

The compiler is the reason ordinary programming exists: without automatic translation from readable code to machine instructions, software as an industry would not have been possible.

You have the invention that made programming possible. What would you ask her?

Ask Grace

• “What does a compiler actually do?”
• “Why did people insist it could not be done?”
• “Why should programs be readable in English?”
• “Why did you keep a backwards clock?”
• “What is wrong with 'we have always done it this way'?”

Chapter 4 · COBOL

A language for people who were not mathematicians

1959 – 1970 · Washington · Philadelphia

By the late 1950s American businesses and the government were buying computers from different manufacturers, and each machine required its own programs. In 1959 a conference convened to define a common business language, and COBOL — Common Business-Oriented Language — was specified in about six months.

Hopper is often called the mother of COBOL. The accurate account is that she did not sit on the short-range committee that drafted the specification, but that FLOW-MATIC was the principal model for it, that she served as a technical adviser to the effort, and that she was its most effective advocate — persuading the Navy, then the wider government, to adopt it.

Her decisive contribution came afterwards. She led the development of validation software that tested whether a manufacturer's COBOL compiler actually complied with the standard. That work turned a specification into a genuine standard, because a program written on one company's machine would run on another's.

COBOL was designed to be readable by managers and auditors as well as programmers, which is why its statements look like sentences. It was mocked for verbosity by academic computer scientists for decades. It also ran, and in many places still runs, the world's banking, insurance and government payroll systems; substantial volumes of COBOL remain in daily production use.

Hopper's teaching device from this period is famous. To explain why signals take time, she handed out lengths of wire 11.8 inches long — the distance light travels in a nanosecond — so that people could hold a unit of time in their hands. She gave away thousands.

Why this matters

COBOL's validation programme established the principle of testing whether an implementation actually conforms to a standard — the basis of software portability.

You have the language that ran the world's ledgers. What would you ask her?

Ask Grace

• “What was COBOL designed to let people do?”
• “How much of COBOL was actually yours?”
• “Why did validation software matter more than the specification?”
• “Why is COBOL still running banking systems?”
• “Why hand out pieces of wire to explain a nanosecond?”

Chapter 5 · Amazing Grace

Retired three times, and promoted to rear admiral at seventy-nine

1966 – 1992 and after · Washington · Arlington

Hopper was retired from the Naval Reserve in 1966 at the mandatory age, an occasion she called the saddest day of her life. She was recalled within seven months for a temporary assignment to standardise the Navy's programming languages, which extended repeatedly. Congress eventually passed special legislation to keep her in service.

She finally retired in August 1986, aged seventy-nine, in a ceremony aboard USS *Constitution*, the oldest commissioned warship in the US Navy — at which point she was the oldest serving officer in the entire American armed forces. She had been promoted to rear admiral by presidential appointment in 1983.

Her later years were spent lecturing, often more than two hundred appearances a year, at universities, companies and military bases. Her theme was consistent: the young should be encouraged and not told that something is impossible, ships in port are safe but that is not what ships are for, and it is easier to ask forgiveness than permission.

After retirement she worked as a senior consultant to Digital Equipment Corporation until shortly before her death on 1 January 1992, aged eighty-five. She was buried with full military honours at Arlington National Cemetery.

A guided missile destroyer, USS *Hopper*, was named for her in 1996 — one of very few US Navy warships named after a woman. She received the Presidential Medal of Freedom posthumously in 2016, and the Grace Hopper Celebration is the largest gathering of women technologists in the world.

Her legacy is a principle as much as a technology: computers should be shaped to fit people, rather than people trained to fit computers.

Why this matters

Hopper's career established the argument that programming should be accessible to non-specialists — the assumption behind every high-level language written since.

You have the whole career. What would you ask her at the end?

Ask Grace

• “Why did Congress pass a law to keep you in the Navy?”
• “What did you tell young people in your lectures?”
• “Why is it easier to ask forgiveness than permission?”
• “What did you mean that ships in port are safe?”
• “Should computers fit people or people fit computers?”

What Grace changed

Hopper built the first compiler and the first English-like programming language, established that computers could translate human-readable instructions into machine code, and drove the adoption and standardisation of COBOL — which still runs a large share of the world's financial and government systems. Her validation software created the practice of testing conformance to a standard.

A debate that continues

Historians of computing take care to distinguish Hopper's genuine contributions from the popular shorthand that credits her with inventing COBOL outright or coining the term 'bug'.

Keep exploring — ask Grace

• “How do you persuade people that something impossible is not?”
• “What did you find hardest about working with the earliest machines?”
• “What should a programming language make easy?”

Related lives

• Ada Lovelace — Enchantress of Number · First Programmer
• Alan Turing — Father of Computer Science
• Katherine Johnson — Human Computer of Langley

Related themes

Programming languages · The history of computing · Women in technology