Oh, I was wasting my time over at slashdot and they had a link to an uk page (I think) with this pic...
And yes, according to the page some Lt. John Gay (honest...sic) won an award for this.
And it's vapor allright... under trans-sonic flight (the "part" of flying when making the transition from sub to supersonic) the differences in air pressures and air speed on the different parts of the plane create shockwaves. This same shockwaves that produce the sonic boom also move the high-pressure, high-speed air over the lower-pressure, lower speed air.
The cloud cone is nothing more than water and other air impurities, compressed and collapsed due to this differences in pressure on trans-sonic flight.(*)
(*) At least that's what I could discern from the lenghty scientifical explanation on the page. I'm sure somebody here in the forum is/was part of some air force or air force related corp or has the sufficient science knowledge to make a correction or denial. Until then, it's 6:30 am, I'm going to bed and I stand by my comments /infopop/emoticons/icon_smile.gif
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This is your brain...
THIS IS YOUR BRAIN ON INF... (bold /infopop/emoticons/icon_smile.gif)