Complex sentence: Even before the "SCR-268" went into service, Harold Zahl was working at the SCL in developing a better system; the "SCR-270" was the mobile version, and the "SCR-271" a fixed-position version.
Split into simpler sentences: Even before the "SCR-268" went into service, Harold Zahl was working at the SCL in developing a better system. The "SCR-270" was the mobile version, and the "SCR-271" a fixed-position version.