In a DARPA news release (11 January 2013) it states they are looking to support the navy by placing hibernated deep-sea capsules with payloads at under water locations and at the seafloor strategically around the globe--"almost half of the world's oceans are more than four kilometers deep" providing "cheap stealth".
The capsules with carry non-lethal payloads for "operational support and situational awareness"--such as command, control, communication, computers, intelligence, surveillance, and reconnaissance (C4ISR).
Examples of pre-deployed payloads could be unmanned aerial vehicles (UAVs) and probably, unmanned underwater vehicles (UUVs). The release specifically states that this is "not a weapons program," but you could imagine future evolutions of this.
The initial capabilities sought are for "situational awareness, disruption, deception, networking, rescue, or any mission that benefits from being pre-distributed and hidden."
The deep-sea capsules will need to survive under extreme pressure and be able to communicate at vast ocean depths to be remotely awoken and recalled when needed.
Having capabilities available when and where needed--from the bottom of the sea to forward deployment--potentially mitigating some use of costly and non-stealth land bases.
I think this is an exciting idea especially since China was able to demonstrate its anti-satellite missiles in January 2007 in shooting down its own satellite, and I would think that these new underwater pods being sought may be able to provide some alternatives for sensing and communicating in conflicts where satellites are destroyed or disabled and/or other military muscle in not readily available.
(Source Photo: here with attribution to Rakel SdPC)