Clayton Webb jokes with Harm that his new assignment could have been worse, he could have been assigned to Canada. David James Elliott is from Canada.
Sadly, in 1968, as here, USS Scorpion (SSN-589) and 99 men became lost in the Atlantic Ocean, about 400 nautical miles southwest of the Azore Islands.
The fictional submarine here is USS Angel Shark (SSGN-559). No submarine of the US Navy has ever borne the name of either Angel or Angel Shark. However, four boats have borne the name Shark, most recently SSN-591, which served 1961-90. Further, no submarine of the USN has borne the number 559.
That number lies in a range, 557-562, which were assigned to six diesel-electric boats, then the order was canceled before construction began. Numbering resumed with USS Tang (SS-563). USS Nautilus (SSN-571), the first nuclear-powered submarine, bears the lowest hull number among the nuclear boats of the USN.
During the Cold War submarines of the USN successfully tapped the undersea telephone cables of the USSR on several occasions in both the Barents and Okhotsk seas. The Soviet Navy captured one of the US devices, and it, complete with its label identifying it as the property of the US government, is still on display in a museum in Moscow.
Although the submarine here is a former SSBN converted into an SSGN, and although the fictional sinking took place in 1968, the first actual such boat was USS Ohio (SSBN-726), which, after her conversion, rejoined the fleet as SSGN-726 on 07 February 2006 -- 38 years after the loss in question.