IBM 1401 Symbolic Programming System
The IBM Symbolic Programming System (SPS) was developed by IBM field engineers [Ray Saunders] as an alternative to the use of machine code for the IBM 1401 computer, the first of the IBM 1400 series. One source indicates that "This programming system was announced by IBM with the machine." [1401 History] It was also used for the 1600 series, the scientific version of the business oriented 1400's. As the 1400 series matured it aquired additonal memory (to 4000 characters from the initial 1400 characters) and SPS evolved into the "Autocoder" language supported by the later 1401's.
Both Autocoder and SPS were assembly languages using mnemonics as a substitute for programming directly in machine language. As such they were among the earliest non machine language programming tools. An example of the 1401 mnemonic operation codes is preserved at 1401.org.
Notes
"1401s I have known" by Tom Van Vleck includes a description of an operating environment including both early, SPS, and later Autocoder 1401 machines.
An Encyclopedia of Computer Languages article entitled "Autocoder III" preserves information from the 1961 announcement of Autocoder programming capabilities for the expanded, 4,000 positions of core memory, IBM 1401.