After the final successful L series flight of August 9, with pressure feed, Goddard turned again to the problem of fuel pumps, which he believed were imperative if very high altitudes were to be attained. This ultimately resulted in the P Series of Tests, which ran from October 17, 1938-October 10, 1941. The work began in the fall of 1938, when he made a thorough study, through more than twenty proving-stand tests, of five models of small, high-speed centrifugal pumps, which had several radically new features. References: 482 .

First static test of James Wyld's regeneratively cooled rocket thrust chambers, which achieved 90-pound thrust. References: 17 .