Cut and paste from another thread:
I'll breathe some new life into this. It seems the RN Fleet Auxillary are also considering versions of the JSS concept as well. The ship will replace bulk cargo, re-fueling etc. They are calling it MARS. [Military Afloat Reach and Sustainability] Note however that MARS is not "a uniform class of ships" but is actually several different ships of varying configuration.
More Information is here: http://www.mod.uk/DefenceInternet/FactSheets/MilitaryAfloatReachSustainabilitymars.htm
and here: http://navy-matters.beedall.com/mars.htm
Requirement
The ‘force projection’ role of the Royal Navy requires three key tasks to be fulfilled by MARS:
Fighting ships to be supplied with bulk consumables (BC) – fuel, food, ammunition, stores, water, and air stores to embarked forces.
Joint sea-based logistics (JSBL) support and sustainment to be provided to land forces from the sea to locations potentially well inland from the beachhead and then sustain their operations.
Forward Aviation Support (FAS) – the provision of support to maritime rotary wing operations. The ships would be able to act as a forward maintenance facility for helicopters.
The forward aviation requirement was re-confirmed in late 2004 after the consideration of other options.
Other MARS roles include supporting:
A CVF centred carrier task group;
An amphibious task group;
Dispersed ships;
A medium sized brigade ashore;
Special forces; and
Joint forces aviation.
It's expected that the MARS ships will need to be able to operate in areas under threat, and some or all will be armed and therefore classed as ‘grey’ or ‘warlike’. Individual MARS ships may operate alone in, for example they could be the assigned unit to Atlantic Patrol Task (North) in the Caribbean, undertaking drug interdiction roles and disaster relief.
MARS will not consist of one uniform of class of ship, but a family of ships perhaps displacing as much as 40,000 tonnes deadweight.