The US Navy allowed the production team to film scenes aboard the Arleigh Burke-class destroyers USS Halsey and USS Dewey as well as the USS Iowa museum ship. The destroyers were sailed several days out to sea so that the cameras could shoot 360 degrees without having to worry about coastlines, buildings, and other ships appearing in the background. Many of the sailors in the background were the crews of those ships going about their duties as cameras rolled.
Even though Tom Chandler, the Commanding Officer of the Nathan-James, holds the rank of Commander, he is called Captain at times because of Naval tradition. That tradition is to call whoever is in command of a Naval vessel Captain, regardless of the actual rank they hold.
Further, since there can be only one Captain on a ship, a Marine captain serving aboard ship, in conversation with Navy officers, is referred to as "Major".
The Italian cruise ship in episode 1 is actually the retired Cunard White-Star Line RMS Queen Mary, a 1936 ocean liner-turned-hotel offering art deco decor, fine-dining & casual eateries, bars & a spa. She's permanently moored in the port of Long Beach, California and has been since 1967.
In June 2016, before a screening of the season three premiere in Washington, DC, Secretary of the Navy Ray Mabus presented the producers, cast and crew with the Navy Distinguished Public Service Award. The honor reflected the show's accomplishment of, in Secretary Mabus's words, "getting the Navy right." While its a fictional portrayal of a Navy ship and crew, Mabus praised the show's ability to capture the culture of the Navy and the dedication of its people to their core values of Honor, Courage, and Commitment.
In Season 2 Episode 7, Alone and Unafraid the rally point 30.275n 81.462w is supposed to be a ballfield. It's actually a golf course and the specific spot is on a lake shoreline. It's just east of Hodges boulevard near Jacksonville Beach.