The Japanese called the P-38 Lightning "Whispering Death"...
because it was so fast and quiet that it could be killing you before you heard it coming. While much smaller than a B-1, the P-38 was also MUCH slower. Coming in fast and low is a good tactic for avoiding detection, even if you're going well below the speed of sound. The closer you are to Mach 1, the less time anyone will have to hear you before you pass overhead.
If you want to hear the sound of a P-38 flying overhead, click here. That's a sound that I can best describe as sexy, but then P-38s always did have that effect on me.