Galactic Patrol by E.E. Smith

Worsel knew his council of scientists, as well he might, since it developed that he himself ranked high in that select circle. True to his promises, the largest space port of the planet was immediately emptied of its customary personnel, which was replaced the following morning by an entirely new group of workmen.

Nor were these replacements ordinary laborers. They were young, keen, and highly trained, taken, to a man, from behind the thought-screens of the scientists. It is true that they had no inkling of what they were to do, since none of them had ever dreamed of the possibility of such engines as they were to be called upon to construct.