Complex sentence: Superconducting computing research has been pursued by the U. S. National Security Agency since the mid- 1950s; however, progress could not keep up with the increasing performance of standard CMOS technology.
Split into simpler sentences: Superconducting computing research has been pursued by the U. S. National Security Agency since the mid- 1950s. However, progress could not keep up with the increasing performance of standard CMOS technology.