MQ-8B Fire ScoutYou need a large f/w UAV capable of covering about 15,000 square miles 50-80 nms ahead of the line of advance. And capable of launching weapons. This roughly replicates what organic fixed wing could do. The P8's would be much further out 100-200 roughly. This constitutes layered defence and the desired detection, location and prosecution of the target would always occur way beyond the screen.
The Fire Scout (even the small one MQ-8B) could deliver sonar bouys. With a 600 pound lift, its not unbelievable that it could also be armed with something like a Mk-54 if required. (not really needed IMO) this is really best handled by MH-60R/P8's.
Even something like the proposed OPV could operate 2 or maybe 3 Fire Scouts each (with 8hr endurance thats 24 hr coverage, just, for short periods). Thus enabling a nearby frigate/destroyer to carry a ready to go, armed MH-60R.