This is how many of some of the most heroic WW2 planes are left

According to a 2014 report by USA Today, 413 World War II vets die each day on average. However, the men (and women) who served in uniform are not the only things vanishing with time.

Many of the planes flown in World War II are also departing one by one from the skies.

In one sense, it may not be surprising – after all, World War II has been over for 72 years. But here are the production totals of some of the most famous planes: There were 20,351 Spitfires produced in World War II. Prior to a crash at a French air show near Verdun in June, there were only 54 flying. That's less than .3 percent of all the Spitfires ever built.

Of the over 15,000 US P-51 Mustangs built, less than 200 are still flyable – about one percent of the production run. Of 12,571 F4U Corsairs built, roughly 50 are airworthy. Of 3,970 B-29 Superfortresses built, only two are flying today.

Much of this is due to the ravages of time or accidents. The planes get older, the metal gets fatigued, or a pilot makes a mistake, or something unexpected happens, and there is a crash.

Finding the spare parts to repair the planes also becomes harder – and more expensive – as time passes. A 2016 Air Force release noted that it took 17 years to get the B-29 bomber nicknamed "Doc" flyable. Kansas.com reported that over 350,000 volunteer hours were spent restoring that B-29.

Many of the planes built in World War II were either scrapped or sold off – practically given away – when the United States demobilized after that conflict.

As David Campbell said in "The Longest Day" while sitting at the bar, "The thing that's always worried me about being one of the few is the way we keep on getting fewer." Below, you can see the crash of the Spitfire at the French air show - and one of the few flyable World War II planes proves how true that statement is beyond the veterans.