Declan is the sonar operator on board the Achilles.

Events of The Last ShipEdit

Declan detects a ship traveling south at a very slow speed and Sean realizes it is the Nathan James. He later notices the ship on passive sonar has disappeared before they can get closer and pick up Juan Carlos. Declan later argues with Max saying firing their torpedoes while they're blind is stupid before Ian breaks it up. Declan then activates the active sonar in preparation to fire on the Nathan James on Sean's orders. After they have fired, Declan warns Sean that the Nathan James has fired their torpedoes and are heading straight for them and they crash dive to avoid them. (“Achilles”)

While the Achilles is being repaired after the crash dive, Henrik discovers the buoy they were using to transmit communications to Sean on land was destroyed. When Henrik suggests warning Sean, Declan advises against rising to the surface as it will paint a target on them. Max says they have to be far enough away based on the fact they haven't heard them in hours but Declan counters that they could be there, they just can't hear them and angrily argues with them before Ian tells them to shut up. Declan eventually sees the Nathan James on radar and concludes from their trajectory that they are heading to their compound on land where Sean is. Ian eventually decides to surface and radio Sean while having Declan verify sonar with flight control. When they reach radio depth Sean gives the order to blow the sub and Ian tells Declan to activate the active sonar in preparation to fire but they disappear from radar before they can launch an attack. (“Alone and Unafraid”)

Declan stands by looking for the Nathan James to sink it once and for all and suddenly hears something off the bottom of the sea but suddenly disappears and asks if they should go active sonar but Sean says no. Declan finally sees them later and Sean asks where it is. Surprised by the location, Declan simply points up, indicating they are right above them. While trying to get out from under them, Max suggests firing but Declan says they are still on top of them and if they try they will be blown up too because of their close proximity. Sean orders him to let them know when they can safely dive and fire their torpedos. When Declan gives the all clear he orders the torpedoes fired and Declan quickly spots four incoming torpedoes incoming and Sean orders an emergency dive and Declan braces for impact.

One of the torpedoes hits the sub and Declan reports that the pressure hull's compromised and they need to surface and Sean tells him to shut up. Declan gives them the Nathan James' location and they prepare to fire when their own rocket battery opens fire on them. Realizing that the sub is going down, Declan screams to abandon ship and tries to with the rest of the crew but Sean and Ned hold guns to them trying to get them to stay, with Sean screaming that they are "chosen". The Nathan James and rocket battery fire consecutively on the Achilles, sinking it and taking the crew, including Declan, with it. (“Cry Havoc”)

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