Jamie Todd Rubin wrote about this story as part of his Vacation in the Golden Age, and I got a pdf copy on Thanksgiving Day in 2012. The story tells of two alien nations at war—a somewhat amateurish was by Martian or Terrestrial standards, but one in which time-traveling weapons target where the enemy was in the past.
The Nyandrians are attacking Strofander with shells which traverse not only space, but time as well.

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  1. “Bombardment in Reverse” by Norman L. Knight, Astounding, February 1940.
    2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . written by Norman L. Knight