With poor British submarine availability, and the only available submarine currently in the Indo-Pacific, it seems far from coincidental that Tourville arrived at Faslane shortly following the transfer of British CASD boats.
This isn't the first time an Allied nation has thought to have picked up the slack due to the consequences of British incompetence. Both American and French submarines are believed to filled this role during the previous periods of British subsurface absence.
The First Sea Lord's '100-day' period for improving submarine availability has now elapsed with none of Astute, Ambush, Audacious or Artful having joined Anson at sea, and Agamemnon yet to start sea trials despite the retirement of Trafalgar-class submarine HMS Triumph in July of last year. The final boat*, Achilles*, remains under construction/fitting out and is not expected to enter service until 2029, by which time construction of the replacement for Astute, the first SSN-AUKUS submarine, is expected to have begun.
With the UK intending the only major fleet increases for the RN to come in the form of five additional SSN-AUKUS boats (as part of an overall 12-boat fleet for the RN), the crisis of availability must be tackled in order to convince British Treasury officials that the MoD, so often caught burning the funds it constantly whines for, to throw good money after evidently bad.
The RN is at its core responsible primarily for the North Atlantic and the Northern Fleet submarine threat. In an era in which money will be tight going forward, hard choice must be made as to what is prioritised.
For example, should the upcoming T31 frigates be equipped with Mk41 VLS, or a form of sonar?
Does the RAF need 12-nuclear armed F-35As (or anymore F-35s altogether), or should those funds go to more P-8 Poseidon MPA?
Does the RN need six monster MRSS, or would cancelling two or three in exchange for additional T26 frigates be a better choice?
Do the upcoming SSN-AUKUS need VLS cells, or would they be cheaper without, and therefore could more be procured?