[Rumil]

A few quick thoughts-

I'd disagree with Galadriel re British use of the word dugout, probably because I'm older (yet another birthday has just passed, but a very enjoyable one!). Dugout would certainly have a military connotation, and more than likely be associated with the First World War, where the front lines were relatively static for so long. This would be a familiar word to Tolkien's generation, to the Second World War generation, and likely their children (due to war films, comics etc).

The times don't fit for the start of The Hobbit, but I guess later on many families might see the hobbit-hole as a reflection of their garden bomb-shelters like the Anderson shelter, though these were often more on the dank, cold and slimy end of the spectrum so I've heard.

The Dead Marshes and Sam's Southron have been mentioned already.

In the early Fall of Gondolin Morgoth unleashes monstrous machines, that have some similarities with tanks and armoured carriers. This reflects JRRT's antipathy for the 'machine', also remember Saruman's devices, including the ent-killling flamethrower-like contrivance.

Tolkien was also dismayed by aerial warfare (despite CT joining the RAF), and I have a theory that the terrifying wails of the Nazgul were suggested by the sirens of Nazi Stuka dive-bombers that demoralised the defenders of France in 1940.

There are also some interesting parallels between the writing of LoTR and course of the Second World War. The story-writing stalled at Balin's Tomb in Moria sometime in late 1940, according to the Foreword. At this time Britain and the Commonwealth stood alone and nobody knew that the Blitz and the U-boat campaigns would, in the end, fail to bring Britain to her knees. Maybe JRRT even considered the book pointless or useless in some way compared with the great struggle proceeding all around him? It's interesting that he continued only in late 1941, by which time both the USSR and the USA had allied to Britain and victory seemed achievable.

I think though, that the main wartime impact on Tolkien is shown by Sam. He seems the ideal 'batman' - an ordinary soldier that accompanied a junior officer and looked after the officer's day-to-day needs in the field, cleaning kit, fetching food etc. To me he represents the 'Tommy', ie the British soldiers in both World Wars. Stereotyped as stubborn, loyal and cheerful and often regarded as possessing more wisdom than their superiors, or at least a more practical sort, as the article that Galadriel posted makes clear.