Originally Posted by
destere
That's not true at all. It could fly supersonically at around M 1.5 IIRC for as long as it liked. It was even allowed to fly at M 2.0 for a limited amount of time. Because of the nature of the promotion (Being around Europe) this wasn't necessary, anyway - that's probably why people think it couldn't fly supersonically, when in fact it really could.
It couldn't do the New York route which was the main constraint. The wings were kept white otherwise it wouldn't have even been able to do the lower speeds.