I understand they did intend -- from what we know now -- to build some sort of engine but the theory was not available to support it so they tried everything to see what sticks -- which was a reference to the EM drive. This is what the search turned out (was surprisingly difficult I'll admit) -- Phil Scranton is a professor of history of technology at Rutger who researched the subject:
"Philip Scranton used the history of the development of jet propulsion in the United
States after 1945 to probe the validity of the linear model, and found little
to no support for it. In critical areas of technology, basic science could not
offer help because it was in too rudimentary a state. Jet engine innovation was
“Edisonian,” Scranton concluded, as “it was a contingent, negotiated struggle with the material world’s
capabilities and limits, a fierce effort to defeat failure along with the Soviets [...]"
This is the original text, Antifragile by Nassim Taleb where I read that first:
"Scranton showed that we have been building and using jet engines in a completely trial-and-error experiential manner, without anyone truly understanding the theory. Builders needed the original engineers who knew how to twist things to make the engine work. Theory came later, in a lame way, to satisfy the intellectual bean counter. But that's not what you tend to read in standard histories of technology: my son, who studies aerospace engineering, was not aware of this. Scranton was polite and focused on situations in which innovation is messy, distinguished from more familiar analytic and synthetic innovation approaches, as if the latter were the norm, which it is obviously not.
I looked for more stories, and the historian of technology David Edgerton presented me with a quite shocking one. We think of cybernetics—which led to the cyber in cyberspace—as invented by Norbert Wiener in 1948. The historian of engineering David Mindell debunked the story, he showed that Wiener was articulating ideas about feedback control and digital computing that had long been in practice in the engineering world. Yet people—even today's engineers—have the illusion that we owe the field to Wiener's mathematical thinking. "