We need something that can be hidden in shipping containers.
Like the Russians Club-K missile system
DARPA also has a program called TEMP (Tactical Expandable Maritime Platform).
I wrote a good part of a proposal for the program for my company; keeping my fingers crossed, should hear in August or September if we won an award.
The DARPA Industry Day slides (unclassifed, approved for public release) are here (warning - a HUGE 13.4 MB PowerPoint, for those with slow connections):
https://www.fbo.gov/utils/view?id=0a698a6419ba49e28482a26856338797
From the first slide:
-A Suite of Modular Technologies that Convert a Commercial Container Ship into a Credible Military Platform
-Meets or exceeds grey hull focused mission capability
-or, delivers fundamentally new capability to the Fleet
-Operates from an unmodified commercial container ship
-Brings all required capabilities in standardized ISO containers
-Embarks modules and goes to sea in 1 day or less
-Conducts mission operations for at least 30 days