What is the USCG ENDGM all about?

A new Mode-S call sign has showed up in some of their MH-65 helos and it is a bit intriguing. We are seeing the Mode-S call sign ENDGM followed by the last two digits of the aircraft serial in some of their MH-65 Mode-S intercepts. The latest list I have is below all from southeast US ADS-B boxes.

AE265E 6504 ENDGM04  2016-01-26 14:59:19 MH-65D United States USCG 

AE2666 6512 ENDGM12  2016-02-09 21:11:09 MH-65D United States USCG

AE2667 6513 ENDGM13  2016-04-03 18:33:50 MH-65D United States USCG

AE266F 6521 ENDGM21  2016-05-02 13:03:39 MH-65D United States USCG

AE2673 6525 ENDGM25  2016-07-12 15:20:11 MH-65D United States USCG

AE2681 6539 ENDGM39  2016-06-08 18:42:45 MH-65D United States USCG

AE268A 6552 ENDGM52  2016-06-08 22:22:50 MH-65D United States USCG

AE269A 6568 ENDGM68  2016-06-10 15:28:10 MH-65D United States USCG

AE26B5 6595 ENDGM95  2016-07-29 19:24:11 MH-65D United States USCG

AE26B6 6596 ENDGM96  2016-02-23 17:57:39 MH-65D United States USCG

AE26BB 6604 ENDGM04  2016-06-21 03:46:07 MH-65D United States USCG

Anybody want to hazard a guess what the USCG is using the Mode-S call sign ENDGM (probably short for End Game) for? Contact me via email at masthead address above.