How Grace Hopper Helped Revolutionize The U.S. Navy

Published December 20, 2017
Updated April 10, 2018

During the Cold War, Grace Hopper changed the way the navy's computer system worked for the better.

Grace Hopper

James S. Davis/United States NavyGrace Hopper

During her time in the United States Navy, Grace Hopper made an astounding number of important technological contributions to this branch of the country’s military. Ironically, she made these contributions after having been deemed unfit to serve.

She first tried to enlist in the navy in 1942 and was rejected because, as a 35-year-old who weighed 105 pounds, she was considered too old and too light for enlistment. Her profession as a mathematician at Vassar College also got in the way of her enlistment, since it was considered to be too valuable to the war effort for her to give up. She countered that she was naturally lean and that she would be able to more directly contribute to the war effort in the navy than at Vassar.

After more than a year, her determination paid off. She succeeded in getting the navy to give her waivers for her age and weight.

She was assigned to the Bureau of Ships Computation Project at Harvard University, where she reported to Howard Aiken. He assigned her to work on the Mark I, the country’s first digital computer.

The Mark I was designed to make mathematical calculations and was programmed using punched paper tape loops. Mechanical feelers would translate the holes in the tape loops into directions for the computer. The navy wanted to use the computer to compute firing tables, which contained data that the military needed to accurately fire ballistic weapons.

Aiken gave Hopper a codebook and demanded that she use it to learn how to program the computer within a week. The problem was that she was a mathematician, not a computer programmer. So she was not exactly cut out for the work that he was demanding of her.

However, she ended up not only mastering the Mark I but she also developed a way to make it more efficient.

Initially, each of the computer’s programs was written from scratch. She felt that this took too much time and effort, so she started using notebooks to write down bits of code that could be reused when needed. She called these bits of code “subroutines.”

Her work with the computer made it not only easier to use but also capable of computing firing tables far more quickly than what the navy had been using to compute them.

The navy had been employing about 100 women with calculators at a research laboratory to compute firing tables. Thanks to Hopper’s programming, the navy was able to abandon this slow and inefficient system and use the Mark I to compute the tables instead.

Following the war, she chose to stay in the navy and worked on the next generation of digital computers, the Mark II and the Mark III.

Univac Console

Wikimedia CommonsThe UNIVAC operator’s console.

In 1949, she helped develop the UNIVAC (Universal Automatic Computer), the first computer capable of translating numbers into letters.

Eventually, computers acquired the ability to store and assemble subroutines by themselves. This led to Hopper’s next major contribution to computer science — the compiler. This was a piece of code that she designed to retrieve and stack subroutines in a computer’s memory and create a program.

An important compiler that she created was FLOW-MATIC, which enabled programs to be written in English and then translated into binary code so that computers could understand them. By 1958, all of the navy’s shipyards were using this compiler.

She retired from the navy in 1966, but was called back to active duty in 1967 to standardize the navy’s computers, doing so until her final retirement in 1986.

Grace Hopper died on Jan. 1, 1992 at the age of 85.

Throughout her career, Hopper used the strong determination that got her into the navy to solve various problems, including her initial lack of computer programming knowledge and the tedium of programming Mark I.

Perhaps more importantly, she was always willing to try out new ideas. As a result, she changed not only the navy but also the world.


Next, read about the six female Nobel prize winners who changed the world, Then learn how the Soviets created a bomb that was too big to use in war

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