The Yellow Jacket 60 racing engines are among the most iconic such powerplants of them all. They were developed by Bruce Underwood beginning in 1955 in response to a growing concern over a series of crankcase failures with the famous Dooling 61 in tether car service. Bruce constructed a long series of them in progressively improved form beginning in 1955. The early examples used Dooling components in Bruce's trade-mark yellow-anodized cases, but by 1965 Bruce was constructing the complete engines himself.

In 1985 the project was purchased from the Underwood Estate by Bob Cowles, who thus acquired the residue of the project but did not actually construct any more engines apart from completing a few almost-finished examples.

In 1994 Bob sold the remaining Yellow Jacket assets to the highly respected engine builder Don Sohn of Oshkosh, Wisconsin. Don has since completed around 70 more engines, two of which are now in my possession along with a sizeable number of others, many of which have been featured in articles on this website. He also completed a number of prototype models which Bruce had designed but only built as one- or two-off prototypes.

In 2022 as he turned 88 years old, Don was understandably becoming concerned regarding the need to ensure that the history of the Yellow Jacket project was not allowed to die with him. With the able assistance of Tim Dannels, the material was organized into a 36 page booklet format. Don subsequently made arrangements with me to have this material appear on my website.  As  result, the Yellow Jacket story may now be found on this site.