Ensign Mason, the ship's sonar officer, says that they will be using ASROC torpedoes to try and destroy the Achilles. ASROC stands for "anti-submarine ROCket", which is an anti-submarine missile system developed for use by surface warships to allow them to attack submarines from extreme range without the enemy submarine being given advanced warning that it would with a traditional torpedo being launched. Traditional torpedoes carried by a destroyer like the Nathan James have a range of less than 10 nautical miles, whereas a ASROC torpedo can have a range of over 20 nautical miles. The original ASROC was a missile fired from a standard horizontal rocket launcher. Arleigh Burke-class destroyer's like the Nathan James are equipped with the RUM-139 VL-ASROC torpedo system which were modified to be fired from the Mark 41 Vertical Launching System that modern guided missile destroyers use; a missile carrying a torpedo is fired from the destroyer's vertical launch tube and has a range of about 20 miles. Once the missile reaches the general area the target is in, the torpedo is dropped from the missile's payload bay and parachutes down to the water's surface. This type of torpedo can give a surface vessel a significant advantage in attacking a submarine as the ship can sit back out of the range of the submarine's passive sonar and launch the ASROC torpedo and the enemy submarine wouldn't be able to detect this launch at extreme range, so the submarine has little to no advanced warning before the torpedo splashes down in the water above it.
Jeffrey Michener used to be Secretary of Housing and Urban Development before the virus, an unforeseen catastrophe, wiped out the rest of the government and he became POTUS. Very much as in Designated Survivor where HUB Sec Tom Kirkman becomes the President after the Capitol bombing during the State of the Union.
The episode's title is an hommage to Eugene O'Neill's 1956 semi-autobiographical drama in four acts "Long Day's Journey into Night".
In one scene CMC Jeter warns Chandler to not let the submarine crew become his "white whale". He is comparing Chandler's desire for vengeance to that of Captain Ahab in the novel "Moby-Dick".
F.I.S. stands for Fire Inhibit Switch, which is a safety system for the ship's missile launch system, saying "FIS is green" indicates that the pre-fire diagnostics on the missile launch system indicates all system's are functioning normally and are ready to fire.