A couple of links on the ME-262.
Normally you'd poo-poo such things, but the interesting thing is that the 262 pilots described what happened to the aeroplane as they apparently went through mach one -
before anyone knew.
And it's documented, so I believe it may well bear further investigation.
http://mach1.luftarchiv.de/mach1.htm
http://www.aerospaceweb.org/question...y/q0198c.shtml