Query: What was a factor in shellac availability?
Context: These were all 78 rpm. During and after World War II, when shellac supplies were extremely limited, some 78 rpm records were pressed in vinyl instead of shellac, particularly the six-minute 12-inch (30 cm) 78 rpm records produced by V-Disc for distribution to United States troops in World War II. In the 1940s, radio transcriptions, which were usually on 16-inch records, but sometimes 12-inch, were always made of vinyl, but cut at 33 1⁄3 rpm.