not initially successful, but by the 1930s had established itself and was regularly publishing science fiction (SF) as well as fantasy. Weird Tales was the first magazine to focus solely on fantasy, and it remained the pre-eminent magazine in this field for over a decade. In the meantime, science fiction was starting to form a separately marketed genre, with the appearance in 1926 of Amazing Stories, a pulp magazine edited by Hugo Gernsback. In 1930 pulp publisher Clayton Publications launched Astounding Stories of Super Science, but the company's bankruptcy in 1933 led to the acquisition of the magazine by Street & Smith. The title was shortened to Astounding Stories, and it became the leading magazine in the science fiction field over the next few years under the editorship of F. Orlin Tremaine. At the end of 1937, John W. Campbell took over as editor. By 1938, Campbell was planning a fantasy companion to Astounding: Weird Tales was still the leader in the fantasy genre, though competitors such as Strange Stories were also being launched. Campbell began acquiring stories suitable for the new magazine, without a definite launch date in mind. When Eric Frank Russell sent him the manuscript of his novel Sinister Barrier, Campbell decided it was time to put his plans into action. The first issue of Unknown appeared in March 1939. It was a monthly at first, but poor sales forced a switch to a bimonthly schedule beginning in February 1941. In December 1940, the subtitle Fantasy Fiction was added, and in October 1941, the main title was changed to Unknown Worlds; both changes were intended to make the genre of the magazine clearer to potential readers. When wartime paper shortages became severe in late 1943, Campbell chose to keep Astounding monthly and cancel Unknown, rather than switch the former to a bimonthly schedule as well. The last issue was dated October 1943. Contents and reception Campbell's plans for Unknown were laid out in the February 1939 issue of Astounding, in the announcement of the new magazine. He argued that "it has been the quality of the fantasy that you have read in the past that has made the very word anathema ... [Unknown] will offer fantasy of a quality so far different from that which has appeared in the past as to change your entire understanding of the term". The first issue, the following month, led with