When the Great Depression hit, the office equipment industry went into free fall, with overall demand plunging by half. But Watson steadfastly avoided disinvestments and layoffs. Citing “demands of the future,” he doubled down on research and development. The strategy would prove prescient, positioning the company to win a huge contract with the new Social Security Administration and enable IBM to engage broadly with the financial services industry. But the most immediate result of Watson’s decision was the 801.

The 801 could sort and list checks, formally verify their authenticity (or “prove” them, in banking parlance) and record totals. For administrators, the handling process was exceedingly simple. An operator would depress the proper sorting key, record the amount on a 10-key adding keyboard, drop the check into a sorting chute, and touch a release bar. Check amounts were listed on an adding machine tape and on a main control tape, which also showed a distribution number. The checks were imprinted with endorsements, identification numbers and dates before being deposited into a sorting receptacle. All items would be listed in their original sequence and totaled by deposit group, with the entire system instantly revealing any errors.

The 801 had an immediate impact on the banking sector. By replacing handwritten teller sheets, the machine (and its successor, the 803) dramatically accelerated the check-clearing process while reducing human errors. Within four years, IBM had installed nearly 500 systems for 140 clients. Check writing began to soar in the US, doubling between 1943 and 1952. With a bespoke pound-sterling keyboard for the UK and Australian markets, the 801 flourished there, as well.

As these technologies and their associated efficiencies took hold, they began shifting the culture and operations of banking, opening opportunities for growth and lowering traditional barriers. Savings and loan companies entered the mortgage business, and commercial banks began offering checking accounts. Dix Gedney, a manager of IBM’s finance industry programs, summarized the sea change in 1973: “Banks are behaving more like businesses than ever before. In so doing, they are making drastic revisions in the way they operate. To accommodate their changing requirements, we’re offering tools and techniques that they can get only in the data processing industry.”

Fuller died in 1943, but successors at IBM continued to build upon his work. By 1949, human check processors using an IBM Proof Machine could input payment amounts and bank identification numbers with one hand while feeding checks into a slot with the other. The IBM 803 Proof Machine, introduced in 1961, featured 36 pockets into which the machine sorted checks for return to the bank on which they had been drawn. A record of the activity would be printed on paper tapes. An adept 803 operator could process up to 1,500 checks per hour. By 1963, IBM had increased that rate to 50,000 per hour with the introduction of a high-speed bank “transit system” that was designed for use by US Federal Reserve banks.

The true legacy of the IBM 801 is apparent throughout modern banking and finance. The machine whet the industry’s appetite for automation and paved the way for a raft of new technologies, many of which were developed by IBM, designed to create a better consumer experience. The first automated teller machine would appear in 1967, with IBM’s version following in 1973. The company also developed magnetic stripe data storage, which enabled credit cards to proliferate, and the self-service kiosks and touch screens that can be found everywhere from airports to ticket counters to grocery checkouts. All of these technologies and innovations are, in various ways, descendants of the IBM 801.

In 1940, Fuller was named a “modern pioneer” by the National Association of Manufacturers, the honor based on outstanding contributions to the creation of “new jobs, new industries, new goods and a higher standard of living.”