423 Maritime Helicopter Squadron is the East coast operational Sea King squadron.

Air crews, maintainers and helicopters form up to eight helicopter air detachments (HELAIRDET) ready to deploy to sea in support of Maritime Operations Group One based in Halifax, Nova Scotia.

423 Squadron is equipped with the CH-124 Sea King ship borne helicopter to support the Navy's Halifax-class patrol frigates and Trump-class destroyers. Domestically, 423 Squadron carries out maritime patrol in Atlantic and Arctic waters in support of other federal agencies such as law enforcement and Fisheries. Search and Rescue in the Maritime region has become increasingly important.

Internationally, the Squadron supports Navy operations in surface and subsurface surveillance, peacekeeping and humanitarian missions.