The shots of the submarine under water and of the emergency blow, as well as the landing of the helicopter, are from The Hunt for Red October (1990). They were all performed by the USS Blueback, which was eventually retired to serve as a stationary exhibit at OMSI (Oregon Museum of Science & Industry) in Portland, Oregon.
Special Agent Timothy McGee was first introduced in this episode.
First appearance of Tony in a suit, which became his trademark style of dress.
During a waterfront scene, ostensibly in Norfolk, in the background there's a ship bearing the hull number AE-31, which was USS Chara, a cargo ship of the Andromeda class, which served first as AKA-58 (an attack cargo ship, 1944-59), later as AE-31 (an ammunition ship, 1966-72). However, on 12 November 1972 the Navy sold the real Chara for scrap.
This is the first appearance of Sean Murray. He previously appeared on JAG (1995) as Danny Walden in five episodes and as Ensign Terry Guitry in one episode, which is the series that NCIS (2003) is a spin-off of. He is also the stepson of both series' creator Donald P. Bellisario.