Seemed like RM boats and another thread for hovercraft is rather too restrictive, when warships (and auxiliaries) being designed and built should keep up with the Joneses, like the USN, and be able to handle anything unmanned (surface or below-surface) as the mission sets for those seem to know of no boundaries.
Without passing any judgement, but just as a teaser one could note the dimensions (and missions) for what the USN sees as a "Common" - for commonality of not just the platform but launch methods to accommodate any such whenever and where ever needed - USV:
"The unmanned vessel has self righting capability and offers high maintainability, as well as reliability. It is equipped with an autonomous launch, tow and recovery system. It is compatible with both LCS configurations, with a length of 39ft, a beam of 10.25ft, draft of 2.2ft and towing capacity of 5,000lb at speeds of 10k.
The Common Unmanned Surface Vessel is equipped with a large, versatile payload bay, which is 14ft-long, 6ft-wide and 3.5ft-high. The payload bay can be integrated with side-scan sonar, intelligence, surveillance and reconnaissance (ISR) payload, mine neutralisation module, and non-lethal weapons. A camera / radar mast is fitted to provide improved surveillance and target acquisition.
The CUSV system also includes KVH TracPhone V7 satellite communications, autonomous maritime navigation equipment and retractable antennae. The payload bay can be reconfigured with a variety of interchangeable payloads to meet multiple mission needs."
- OTH (or near to it) operating does not need to be a From-Day-One requirement, but once in place cued tracking of subs could easily be added (a sub-function could be acting as a comms relay for sonobuoys that have been deployed by other means)