I'm not sure how to describe this, but the problem came about as I was computing some acceleration profiles. Let's say you want to get up to Mach 3 (939 m/s) quickly. If you accelerate at 3 g's, this will take 31.923 seconds (not bad), and in level flight would cover a ground path of 14.991 km (kind of a lot, but not really comparable to typical flight lengths).
Only problem is, when it comes time to land, you have to slow down. If you want to do that quickly too, well, 3 g's in the "eyeballs-out" direction is a little hard on the eyeballs. Doing 1 g would take 3 times longer but also cover a ground path more than three times longer because of that pesky time squared in the equation for uniform acceleration ($\Delta x = \frac12 at^2$, if initial x and inital v are zero).
So you could gradually slow down over an even longer distance, or...is there some other, quicker way that doesn't involve much eyeballs out? Could you maybe fly a circle over the airport and decelerate that way, so that you feel the g-force mostly pointing down into your seat? Is there some other way you could "cut into another plane"?
The goal is to decelerate quickly so that the average flight speed (over the whole journey) is very close to Mach 3.