In the history of Caterpillar, there was an engine that had profound significance and changed the entire industry. It is "Old Betsy". "Old Betsy" is the nickname for Caterpillar's first handmade diesel engine prototype. In 1931, the invention of "Old Betsy" — CAT D9900 almost overnight changed Caterpillar and the entire industry, representing Caterpillar's initial energy transformation from gasoline to diesel power.

In fact, before Benjamin Holt and C.L. Best decided to merge their companies to establish Caterpillar, they had already begun studying the feasibility of assembling diesel engines in earthmoving machinery. In 1915, Best had the idea of installing a diesel engine on a bulldozer after attending the World Expo held in San Francisco. The design and development of 'Old Betsy' began in 1927. Even during the special period of the 1930s, the leaders of Caterpillar insisted on investing in diesel technology. The reason why they continued to invest in diesel technology is that they recognized that diesel engine performed better than gasoline engine. Diesel engine could offer greater output torque and it's more fuel-efficient. The "Old Betsy" engine was assembled in June 1930 in San Leandro, California, with serial number 1A14. After more than 16 months of testing, it was deemed ready for production in late 1931.

Initially, "Old Betsy" mainly provided power for Caterpillar bulldozers. In October 1931, Caterpillar began producing the first bulldozer model equipped with a diesel engine — the "Caterpillar 60 Diesel Bulldozer". In the mid-1930s, Caterpillar became the world's largest diesel engine manufacturer, and diesel technology became the company's core business at that time.

In 1973, "Old Betsy" was donated to the Smithsonian's Museum of American History after being repaired and passing a series of strict emission tests. Due to its highly forward-looking design, even 40 years after its birth, "Old Betsy" could still almost meet the emission standards of 1973.

1931 was a year of innovation in Caterpillar's history. In addition to the first diesel engine of the "Old Betsy", there were also several firsts and milestone innovations in its history. To this day, Caterpillar is still on the path of innovation, continuously investing in new products and technologies to help customers in energy transformation, and moving forward in building a better and more sustainable world.