Factual error: "The Phantom Strikes": The Seaview's military history computers need an upgrade. The derelict German sub is identified as a WWI ship, the U444, supposedly sunk in 1918. There were only 167 U-boats in WWI. U444 wasn't built until 1942. And the sub's design is definitely WWII, not WWI.
Factual error: "The Phantom Strikes": The derelict sub is said to have suddenly moved itself more than 30,000 sea miles from its original position. This makes no sense. The entire circumference of the Earth is only 22,000 sea miles. And if the sub had somehow circled the globe plus an additional 8,000 sea miles, there'd be no way to tell that it hadn't simply moved just 8,000 miles.
Factual error: "Killers of the Deep": Due to the extensive use of borrowed footage from the WWII film "The Enemy Below," the 1970s crew of the renegade sub (who are not German and who wore civilian clothes in most shots) suddenly acquire 1940s German U-boat caps and uniforms.
Factual error: "No Way Out": Victor is crawling around through Seaview's incredibly roomy ventilation ducts, pursued by several crewmen. But the air conditioning that's fluttering little ribbons on all the vent covers isn't, for some reason, disturbing a hair on any of their heads.
Factual error: "Invaders": The ship's doctor claims that carbon 14 dating proves the man from the undersea capsule to be 20 million years old. Not likely. Carbon 14 testing can date once-living matter only within the last 70,000 years, and is generally considered accurate only within the last 50,000.