After the robots first attack New York City, a series of newspapers is shown. On the Japanese one, you can see Godzilla's outline.
When Joe is going to shoot the bomb on the robot's legs, you can see King Kong climbing on the Empire State building in the background.
Totenkopf (German for "death's head") is a military insignia featuring a skull above crossed bones and that the lower jaw bone is absent. Today the insignia is particularly associated with Nazi Germany's elite soldiers who served in the 3rd SS Panzer Division (Death's Head Division) in World War II, but it has its origins in cavalry of the Imperial Prussian army.
Dr. Totenkopf is played by Sir Laurence Olivier, who died in 1989. Kerry Conran achieved this by using computer manipulated archive footage of Olivier and pictures given by his family.
Director Kerry Conran never went to New York City during the production. The city is digitally recreated by using old pictures, some of which used as backgrounds in the film.
When Polly is reporting the advance of the giant robots on the phone to her editor, she says "They've reached Sixth Avenue... they've reached Fifth Avenue... they're a hundred yards away..." This is an exact line taken from the famous 1938 radio adaptation of "The War of the Worlds," with Orson Welles.
At first, the title was simply "The World of Tomorrow," but has been changed so as not to be confused with another 2004 production, "The Day After Tomorrow."
On the entrance door of Dr Walter Jenning's laboratory, it's written "Suite 1138," a reference to THX-1138 (1971), directed by George Lucas.
While in the underwater scenes, viewers can see two famous ships: the "Venture" which carried King Kong and the "Titanic."
Kerry Conran first started this film with a low budget. He wanted to make a film with his friends and his family in his house, but it became too long to achieve. Producer Jon Avnet heard about the six-minute film and was deeply impressed, so he approached Conran with the idea of turning it into a full-length production.
When the army send an emergency message to Joe Sullivan, the call comes from a huge radio tower sitting on the top of the Earth and consists of visible radio waves. It is a reference to RKO Radio Pictures' logo.