At the beginning of the Revolution the Council of Safety asked that he should "prepare moulds for the casting of clock weights, and send them to some iron furnace, and order a sufficient number to be immediately made for the purpose of exchanging them with the inhabitants of this city for their leaden clock weights." The leaden weights were needed for bullets. Later he was sent to survey the shores of the Delaware, to choose the best points for fortifications.
When he became Engineer of the Council of Safety "he was called upon to arrange for casting cannon of iron and brass, to view the site for the erection of a Continental powder mill, to conduct experiments for rifling cannon and muskets, to fix upon a method of fastening a chain for the protection of the river, to superintend the manufacture of saltpeter, and to locate a magazine for military stores on the Wissahickon."
This was but the beginning of service to Pennsylvania during the Revolution. His activities were so valuable to the Colonies that a Tory poet published in the Pennsylvania Evening Post of December 2, 1777, a verse addressed "To David Rittenhouse," of which the first stanza read:
"Meddle not with state affairs,
Keep acquaintance with the stars;
Science, David, is thy line;
Warp not Nature's great design.
If thou to fame would'st rise."
The following year Thomas Jefferson wrote to him:
"You should consider that the world has but one Rittenhouse, and never had one before.... Are those powers, then, which, being intended for the erudition of the world, are, like light and air, the world's common property, to be taken from their proper pursuit to do the commonplace drudgery of governing a single State?"