just had a read through Jnes us miltary aircraft here goes cantelever monoplane wings variable picth props retractable undercarrage and stressed skin construction
Very simply, when it came out, the B-10 was the most advanced bomber aircraft in the world, and was quite a bit faster than any fighter aircraft then in service....
It was Un-Interceptable, and remained so for about four or five years...
Here's a vid::::::::::::::
And another vid:::::::::::::
Things were moving ahead so fast in those days, though, that by the time WWII arrived, they were obsolete!