use the f-15 (any) on free flight, hit the AB's and ascend to 45,000 feet. Then hit the AB's and pitch your jet to zero whiskey, and you will see the mach meter fly from 1.0 to 2.3, 2.3, and up to the max. Used only with the advanced jet setting.

Also, even though your mach speed is going up very fast, your engine readout (speed readout) will probably be rising slowly, like it would say 850 and you'd be mach 2. I beleive the readout is programmed to read the speed of engine output, not how fast you are really going. (then again, when you dive and have engine speed at zero, it does count that dive speed...maybe they kept it for dive bombing?) Anyhow, the difference in the air at that altittude would cause AB's to provide real pushing power. I tried hard to get to Mach 2 on the ground, in the bay area. I was using the 'stay on gears and dont overspeed' trick, and made it to mach 1.83 before i stopped moving. I tried it in the air at 20,000 or so and still got nothing. THen i rembered in ace combat if you climbed to 40,000, your AB speed gave you the best boost at that altittude. So I tried it, and it worked, and i think i got the jet made from scrap f-104j parts, the red and white remote version. (the uf..something?)

also, if you reach 50,000 or higher, you get some other jet, i think its the f-104j.

You can do it with the following aircraft

F-14
F-15 (any variant)
F-2

THat's all that i got confirmed so far

Most of the jets that have info saying you can reach mach 2 as the max speed limit might be able to do it, but you have to have a steady hand and overspeed just a little, about at a negative 5 pitch. You should get the mach meter to 2 before it drops. Anything with over mach 2 as max speed can also get it easily at max alltitude. I also tried going straight up, then heading straight down, from 60,000 feet, but weird enough, the mach meter only dropped, even though my speed went over 850kts. ???

The the unmanned one the UF-104 and you unlock the UF-104
by going above 50,000 ft (reminder)