This is not the new Advanced Seal Delivery Vehicle. That was cancelled. This is the older, "wet" SEAL delivry vehicle. What you see is an enclosure, mounted to the sub over one of the lock-in, lock-out tubes, for them to access the mini-sub which is inside.
Thanks Jeff! I did not know that. I learn something new nearly every day.
ARABIAN GULF (Oct. 10, 2014) Aviation Boatswain's Mate 3rd Class Matthew Reyes, from New York, observes flight operations from primary flight control aboard the aircraft carrier USS George H.W. Bush (CVN 77). George H.W. Bush is supporting maritime security operations, strike operations in Iraq and Syria as directed, and theater security cooperation efforts in the U.S. 5th Fleet area of responsibility. (U.S. Navy photo by Mass Communication Specialist 3rd Class Joshua Card/Released)
ARABIAN GULF (Oct. 10, 2014) The amphibious assault ship USS Makin Island (LHD 8) is underway in the Arabian Gulf. (U.S. Navy photo by Lt. Juan D. Guerra/Released)
ARABIAN GULF (Oct. 10, 2014) The amphibious assault ship USS Makin Island (LHD 8) pulls alongside the aircraft carrier USS George H.W. Bush (CVN 77) for a vertical replenishment. George H.W. Bush is supporting maritime security operations, strike operations in Iraq and Syria as directed, and theater security cooperation efforts in the U.S. 5th Fleet area of responsibility. (U.S. Navy photos by Lt. Juan D. Guerra/Released)