[dingaling]

And for each US domestic rotation each individual aircraft was reregistered onto the US N-register, and then back onto the UK or French register for the Atlantic crossing.

At that time only N-reg aircraft were pemitted to operate internal commercial US flights.

To simplify the process the BA Concordes were allocated unique-for-the-UK alpha-numeric registrations which could have their 'G-' prefix hidden by speed-tape:

http://www.braniffpages.com/n94aa.jpg