More soberly this is the US Defense Advanced Research Projects Agency (DARPA) Upward Falling Payloads (UFP) Program consisting of pods laid first by US Navy ships, subs, aircraft or by large UUVs. Then:
1. perhaps months or years later if a Threat (like a passing ship or sub) emerges a Trigger (perhaps triggered by passive sonar or remotely triggered from a US Base) will
2. release the pod (called the "Riser") from the seabed or from its tether. The Riser floats up near to the surface or to the surface and then releases
3. the Payload, which may be a group of very small UAVs or UUVs then unfurl their wings or fins and start moving toward the Target.