Notes: • © 1951, no other date, printing or number line • Printed at least twice with the same catalog # • Date from ads in the back: 7 and 17B; 7 changed to 7A before June 1973, 17B was in use from early 1973 until at least mid-1974 • "A condensed version under the title Planets in Combat appeared in three parts in Blue Book Magazine." • Cover art by Steele Savage on copyright page, the artwork is also signed • Frontispiece by Clifford Geary on copyright page, no visible signature on the piece