U.S. Sailors prepare a close-in weapons system to receive ammunition on the fantail of USS Essex (LH D) Sept. 19, 2008, while under way in the Pacific Ocean. Essex serves as the flagship for Combined Task Force 76, the Navy's only forward-deployed amphibious force. (DoD photo by Mass Communication Specialist 2nd Class Greg Johnson, U.S. Navy/Released)

That’s a Block 1B Phalanx CIWS. The major exterior differences between it and earlier models are the reinforced barrels assembly and the FLIR/video pod on the left side. The Block 1B has been optimized to engage surface targets such as boats and slower aircraft like helicopters.

Here’s a summary of the Phalanx’s evolution:

Much more info on the Block 1B and more at CIWS now does surface targets, too.