Seems logical. If the alternatives are to either build another medium orbit navigation constellation (it would be the fifth!) or to try and build something dif

Seems logical. If the alternatives are to either build another medium orbit navigation constellation (it would be the fifth!) or to try and build something different and then trade access to that to the US for guaranteed GPS access, then that makes sense. If they just built a GPS/Galileo/Glonass/Beidou clone then they'd have nothing of strategic interest to trade access to (and it would be horrifically expensive). A regional solution like NavIC or QZSS would also not be of use to trade and wouldn't provide service over the whole operational footprint of the Royal Navy. On the other hand, since the US military does not have a low earth orbit GNSS system (nobody does), it becomes tradeable for privileged GPS access. The same way that the UK can genuinely trade the US access to a small number of specialist military assets that the US either does not have or has a shortage of but cannot trade on total force capacity (since obviously the UK military is vastly smaller).