Retrofit (verb): to renovate or add capability, while maintaining the original purpose.
In mid-20th century, homes, buildings, planes, and other manufactured designs were being produced and implemented at a slower rate that knowledge was being produced. For example, in the USA there were homes across the country that were considered operational and fine. Yet with the advent of rapid cement construction used in American colonial settlements, construction preceded geographical, geological, and ecological understanding of the world around their settlements. In the case or tech and airplanes, rapid scientific development of more efficient or completely new technologies out-paced production time. This necessitated in adding the new parts into the design that was intended for parts that were less efficient.