Isnt this the last one? How many other birds are they putting up as part of the net?
This is the freebie. The insurance costs for A and B were so high they decided it was cheaper to build and launch a spare instead. The first 2 fly OK, so this adds extra capacity.
(Because it's a PFI, they can sell the extra capacity on the civil market if we don't use it, which makes it a good commercial proposition to build and launch it - they took the chance, and they won - good luck to them...)