Answer by taking a quote from the following article:

Isaac Asimov (; c. January 2, 1920 - April 6, 1992) was an American writer and professor of biochemistry at Boston University. He was known for his works of science fiction and popular science. Asimov was a prolific writer who wrote or edited more than 500 books and an estimated 90,000 letters and postcards. His books have been published in 9 of the 10 major categories of the Dewey Decimal Classification.

Asimov attended New York City public schools from age 5, including Boys High School in Brooklyn. Graduating at 15, he went on to Seth Low Junior College, a branch of Columbia University in Downtown Brooklyn designed to absorb some of the Jewish and Italian-American students who applied to Columbia College, then the institution's primary undergraduate school for men with quotas on the number of admissions from those ethnic groups. Originally a zoology major, Asimov switched to chemistry after his first semester as he disapproved of "dissecting an alley cat". After Seth Low Junior College closed in 1938, Asimov finished his BS degree at University Extension (later the Columbia University School of General Studies) in 1939.  After two rounds of rejections by medical schools, Asimov in 1939 applied to the graduate program in chemistry at Columbia; initially rejected and then accepted only on a probationary basis, he completed his Master of Arts degree in chemistry in 1941 and earned a Doctor of Philosophy degree in biochemistry in 1948.  In between earning these two degrees, he spent three years during World War II working as a civilian at the Philadelphia Navy Yard's Naval Air Experimental Station, living in the Walnut Hill section of West Philadelphia from 1942 to 1945. In September 1945, he was drafted into the U.S. Army; if he had not had his birth date corrected, he would have been officially 26 years old and ineligible. In 1946, a bureaucratic error caused his military allotment to be stopped, and he was removed from a task force days before it sailed to participate in Operation Crossroads nuclear weapons tests at Bikini Atoll. He served for almost nine months before receiving an honorable discharge on July 26, 1946. He had been promoted to corporal on July 11.  After completing his doctorate and a postdoc year, Asimov joined the faculty of the Boston University School of Medicine in 1949 with a $5,000 (equivalent to $51,427 in 2017) salary, with which he remained associated thereafter. By 1952, however, he was making more money as a writer than from the university. The difference grew, and in 1958 Asimov stopped teaching to become a full-time writer. Being tenured, he retained the title of associate professor (which he had held since 1955), and in 1979, the university honored his writing by promoting him to full professor of biochemistry. Asimov's personal papers from 1965 onward are archived at the university's Mugar Memorial Library, to which he donated them at the request of curator Howard Gotlieb.  In 1959, after a recommendation from Arthur Obermayer, Asimov's friend and a scientist on the U.S. missile protection project, Asimov was approached by DARPA to join Obermayer's team. Asimov declined on the grounds that his ability to write freely would be impaired should he receive classified information. However, he did submit a paper to DARPA titled "On Creativity" containing ideas on how government-based science projects could encourage team members to think more creatively.

What was his first job
Philadelphia Navy Yard's Naval Air Experimental Station,