Let's begin at the beginning:
In a hole in the ground there lived a hobbit.
No, that's not the beginning. For understanding J. R. R. Tolkien and the aeroplane, the beginning is the Great War. He may have seen one flying overhead at Birmingham, where he grew up and went to school, or at Oxford, at which he enrolled in 1911. But they were quite rare birds at this time, and Tolkien doesn't seem like the sort of young man who would have been particularly interested in them. He probably would have encountered them when training as an Army officer in 1915, or, at the very latest, when he was posted to frontline service in France in July 1916.
Here Tolkien was thrown into the thick of things, as a signals officer in the 11th Lancashire Fusiliers fighting on the Somme, and aeroplanes were a common sight (there was a dogfight over the village where he was billeted when he arrived at the front). But the only trace of anything aeronautical in his writings at this time are blimps. These seem to have made quite an impression on him. In 1924, he recalled that 'German captive balloons ... hung swollen and menacing on many a horizon'.1 Perhaps he thought they were menacing because they made him think of some weird monster; but they were also menacing in a more direct way, because observers in the balloons recorded British positions and movements, for use in German counterattacks and barrages.
But Tolkien's interest was philological too. After the war he speculated that the world 'blimp' was a portmanteau word deriving from 'blister' and 'lump': 'the vowel i not u was chosen because of its diminutive significance -- typical of war humour'.2 But more significantly, in a lexicon he worked on during the war for his invented Elvish language, Quenya, he added an entry for pusulpë, 'gas-bag, balloon'.3 This was probably added sometime after the Somme and so would seem to be inspired by the 'swollen and menacing' German balloons he had seen: an obvious connection between Tolkien's war experience and his developing legendarium (all the more so because, as far as I'm aware, Elves are not known for their ballooning).
There's another clear influence of the technology of the Great War in Tolkien's work at this time, one involving dragons destroying a city. Unfortunately for me, the technology in question is not the aeroplane but the tank. Having come down with trench fever after the Somme, Tolkien wrote 'The Fall of Gondolin', the first of his many prose tales of Middle Earth, in 1917 while convalescing back in Blighty. Gondolin was a city of the Noldor elves, founded by Turgon the Wise in the First Age. It was betrayed from within and fell to the forces of Melko (better known as Morgoth, Sauron's master). John Garth argues that Melko 'represents the tyranny of the machine over life and nature, exploiting the earth and its people in the construction of a vast armoury'.4 Key to Garth's argument here are Melko's dragons, which appear to be more machine than flesh. I'll quote Garth's passage on them in full here, as he quotes Tolkien extensively:
'From the greatness of his wealth of metals and his powers of fire' Melko constructs a host of 'beasts like snakes and dragons of irresistible might that should overcreep the Encircling Hills and lap that plain and its fair city in flame and death'. The work of 'smiths and sorcerers', these forms (in three varieties) violate the boundary between mythical monster and machine, between magic and technology. The bronze dragons in the assault move ponderously and open breaches in the city walls. Fiery versions are thwarted by the smooth, steep incline of Gondolin's hill. But a third variety, the iron dragons, carry Orcs within and move on 'iron so cunningly linked that they might flow ... around and above all obstacles before them'; they break down the city gates 'by reason of the exceeding heaviness of their bodies' and, under bombardment, 'their hollow bellies clanged ... yet it availed not for they might not be broken, and the fires rolled off them'.5
Garth quotes a number of contemporary accounts of the tank -- which of course was a new British weapon which made its debut at the Somme -- to show how it was already seen by others as a kind of mythical beast. (One he misses is my favourite: 'A tank is walking up the High Street of Flers with the British Army cheering behind', my italics.) Tolkien was doing the same, just using his own original mythology to understand the new warfare.
But what about the aeroplane? Did Tolkien mythologise this too? I'll try to answer that in another post.