Watts' Double-acting steam engine. The Watt steam engine (alternatively known as the Boulton and Watt steam engine) was the first type of steam engine to make use of steam at a pressure just above atmospheric to drive the piston helped by a partial vacuum. Improving on the design of the 1712 Newcomen engine, the Watt steam engine, developed sporadically from 1763 to 1775, was the next great step in the development of the steam engine. Watt's two most important improvements were the separate condenser and rotary motion. Illustration from A review of American progress by Theodore Dwight Woolsey, 1876.