The Battle of Dorking
Chesney, Sir George Tomkyns. "The Battle of Dorking." Published anonymously in Blackwood's Magazine May 1871 "and subsequently republished in numerous special editions," under differing titles (including The Battle of Dorking: Reminiscences of a Volunteer) and in translations into French, German, and Portuguese: see I. F. Clarke's Voices Prophesying War pp. -26 and passim.
Dorking may not be the first-written future-war story, but according to Clarke it set the pattern for a new genre and started that genre really going. The main relevance here for "Dorking" is that the time was ripe for such stories not just because Europe and other parts of the world were moving into a pathological nationalism but also (perhaps paradoxically) because of great technological developments — especially steam power and the telegraph — and the hope and confidence that there would be more. "Before The Battle of Dorking, no author of an imaginary war of the future ever suggested that the deliberate use of new weapons and technological devices could have a decisive effect on the outcome of a battle or a war" (Clarke ch. 1, p. 3; see also ch. 2, pp. 45-47).
In a chapter called, significantly, "The Battle of Dorking Episode" (ch. 2), Clarke notes that
Technology was behind the whole process of advance as it was seen and felt by the Victorians. Technology provided the power and the equipment for incessant change; it was a major source from which the nineteenth century found evidence for the doctrine of progress; and it had a decisive influence on the establishment of the new futuristic fiction that began to spread through Western literature after 1800. All the great advances, from the steam engine and the railway to the laying of the Atlantic Cable, the opening of the Suez Canal, and the ending of cholera epidemics, had helped to convert the evident fact of change into the dogma of unending progress. [* * *]
Within a generation of the first balloon ascents and the first steam engines, a new literature of futuristic fiction had begun to emerge in Europe: steam balloons, steam ploughs, passenger kites, and electrical road vehicles were to be expected, so writers imagined, in the very different world of time-to-come. 'Change', 'progress', and 'improvement' were the new catchwords. [...]
Poets agreed with engineers that technological development meant social — and often moral — improvement. (p. 46)
And, of course, the potential for use of that technology for new weapons of war, for glorious conquest, or, as in "The Battle of Dorking" from the side of the ill-prepared English, defeat.
The Royal Navy is destroyed by a wonder-weapon ("fatal engines"), and an invasion force suddenly lands near Worthing, Sussex.
Clarke believes "Those secret weapons" to be "the only weakness in the story," and, more specifically and less judgmentally, "presumably mines or torpedoes" (p. 32).
Demilitarisation and lack of training means that the army is forced to mobilise auxiliary units from the general public, led by ineffective and inexperienced officers. The two armies converge outside Dorking, Surrey, where the British line is cut through by the advancing enemy and the survivors on the British side are forced to flee.
The story ends with the conquest of Britain and its conversion into a heavily-taxed province of the invading empire [Germany, not named in the story]. (Wikipedia entry for "Dorking," plot)
Note that like most of these works, "Dorking" has an agenda, as a work of propaganda pushing more military spending and arming the UK to resist potential invasion by an enemy capable of developing and deploying "fatal engines" that can destroy the Royal Navy as an effective fighting force.
RDE, finishing, 4Dec20