I was a kid living in a FL coastal town during the early days of WWII. We had to black out our windows and car headlights because German subs were operating just a few miles offshore. Ships running along the coast were silhouetted aganst the glow of town lights before the blackouts and were easy targets. Of course we were never actually in danger of being invaded, but the blackouts and reports of ships torpedoed right offshore gave us the impression that the war wasn't that far away.
I spent lots of time planning how I would use my grandfather's single shot .22 rifle to repel invaders if and when they hit our beaches. I think the Germans and Japanese got word of my plans and that's why they never tried to invade.
Well, your's and those of the million of other Amercians who owned firearms. A very large fraction of households in those days. One Japanese Navy and latter JASDF officer is quoted as saying they, or at least their Naval officers who had often studied in the US, weren't so foolish as to try to invade a country where almost every house had a gun, or three, and someone who knew how to use it. A country were every little burg had a shooting range, or at least periodic shooting contests. A country, many of whose people would quite likely ignore any official surrender order.
Add to that .22 the millions of experienced deer hunters' rifles, and you have a very good idea why invasion never entered the plans of Germany or Japan