It is a short story written in
1903 about two unidentified armies dug into trenches, with one side building 100-foot-long armoured fighting vehicles to brake the stalemate.
The uncanny similarities between it and the First World War (Trench warfare, 'Landships', "
Men in Blue Pajamas➡") were not lost to the people of 1916.
It is public domain and can be found
Here and a PDF
Here