If you saw Captain America: The First Avenger, you know the movie is loaded with fantastic, retro-futuristic war machines dreamed up by supervillain Red Skull and his Hydra organization.

Discover how the filmmakers came up with one such vehicle — an escape sub used by a Hydra assassin — in the behind-the-scenes clip above.

Captain America’s lead vehicle designer Daniel Simon outlines several concepts that preceded the streamlined, cigar-shaped sub that made it into the movie.

“We could have gone totally overboard, but that would have made it almost childish, in a wonderful way,” says Simon in the video, taken from the movie’s Blu-ray extras. “But we wanted to be very serious.”

The final underwater vehicle perfectly fits the style of director Joe Johnston’s movie, which is set in a World War II-era world rife with Hydra’s twisted Nazi technology.

All the sci-fi eye candy nicely complements the human drama of pipsqueak-turned-supersoldier Steve Rogers, played by Chris Evans. The movie boasts an all-star cast and is a winning addition to Marvel Studios’ cinematic universe (and a great setup for 2012’s The Avengers, which will team Cap with Iron Man, Thor and the Incredible Hulk, among others).

Wired.com is giving away four copies of the Captain America: The First Avenger three-disc combo. The limited-edition set, which will retail for $55 when it hits stores Oct. 25, delivers the action in Blu-ray 3-D, regular Blu-ray and DVD, and includes a digital copy of the movie.

To enter, leave a comment below naming your favorite scene from Captain America or any other Marvel movie. Deadline to enter is 12:01 a.m. Pacific on Oct. 26, 2011. Four randomly selected winners will be notified by e-mail or Twitter. Winners must live in the United States.

Note: If you do not have an e-mail address or Twitter handle associated with your Disqus login, you must include contact information in your comment to be eligible. Any winner who does not respond to Wired’s notification within 72 hours will forfeit the prize.