I believe the thought is that the E3 would co ordinate a big SAR operation. How often they actual rehearse this complex task and understand the maritime environment and SAR/ Coastguard organisation is debatable.
Sarcasm on...
Oh my God, with a couple of helos and a few boats (on primary RADAR and AIS) how would the mission crews cope with vectoring them to the target area? Especially with its various radios, datalinks and satcom?
Sarcasm off...
The E-3 has proven that it can vector Coastguard cutters and helicopters to intercept small boats carrying stuff that isn't good for your health in the past - I'm sure they'd cope!
LJ