A medium power built around deployable naval groups

How would you use a British defence budget of 5% of GDP for forces, procurement and maintenance?

Build deployable carrier and amphibious groups with escorts, auxiliaries, submarines, cross-deck-capable F-35Bs, airlift, and reserve logistics.

The proposed force starts with separate requirements for global reaction and European reinforcement. A Royal Marines brigade and carrier group would be available continuously, backed by air-mobile and strike formations. Four Queen Elizabeth-class carriers, four LHDs and four LPDs would support that readiness cycle, with larger escort, submarine and auxiliary forces around them. F-35Bs would share carrier and LHD decks so aircraft could divert, refuel and rearm across the force. Airlift would seize an airfield in conjunction with an amphibious landing and sustain it until the sea connection opened. This is a preferred force structure for the budget hypothetical, rather than a costed programme.