There was a fourth bomber [1] in case there had been any delays with the three types that went into production. None of them were supersonic though. [1] https:

There was a fourth bomber [1] in case there had been any delays with the three types that went into production. None of them were supersonic though. [1] https://en.wikipedia.org/wiki/Short_Sperrin https://en.wikipedia.org/wiki/Short_Sperrin