Super new whiz-bang attack submarine which will replace the remaining Swiftsure class, and eventually the Trafalgar class too. Unfortunately it's being made by BAE, so it's massively late and over budget.
The Astute class of SSNs (Ship, Submersible, Nuclear - don't call them 'Hunter-Killers' as it's chad) will consist of 6 platforms - ASTUTE, AMBUSH, ARTFUL, AUDACIOUS, ANSON and AGAMEMNON when the build programme finally shudders to a halt.
They are much larger than their S Boat and T Boat predecessors (aound 8000 tonnes displacement compared to 3-4000 ish)owing to their use of the Rolls-Royce PWR2 nuclear reactor as designed for the VANGUARD-class SSBN (Ship, Submersible, Ballistic, Nuclear - again, don't call them 'Bombers' or 'Boomers' which carries a high chadness factor). BAe, as always, managed to turn this to disadvantage, and by means of modular build of hull internal sections, left huge amount of internal void space useable by no-one. This renders an ASTUTE class boat like the TARDIS but the wrong way around, and in spite of displacing the same as a WW2 cruiser, its crew are rammed into any vacant spaces like illegal immigrants in a Ford Transit on a car ferry.
Apart from this, the ASTUTE class have some impressive innovations. A non-hull penetrating optronic periscope uses state-of the art technology to allow the command team to see what's happening on the surface via display screens, and there is one less massive hole in the pressure hull. Submariners don't like holes in the pressure hull - they can sometimes let water into the people tank and this is sub-optimal. The best part of the optronic perisope is that periscope watchkeepers no longer cut around the submarine like Jurgen Prochnow with their stopwatches around their necks like they've just ambushed a convoy or something. They (ASTUTE-class, not periscope watchkeepers)are also fitted to support the CHALFONT Special Forces delivery system, which is massively Ally.
Sadly, the Ship's crests are pants. AMBUSH has an image of a bush with spears sticking out of it, and ARTFUL's features some kind of primate.