How cool would it be to own your own submarine? Of course, submarines are very expensive. They’re also very large. You’d need a lot of water to be able to have fun with it. The average bathtub just wouldn’t do.

If you had a submarine, where would you go? Searching for sharks? Exploring the depths of the Mariana Trench or the mysterious Bermuda Triangle? The depths of the sea contain many unexplored frontiers, so your adventures could be never-ending!

Every once in a while, you’d probably want to come up to the surface to see what’s going on above water. But how would you do that in a submarine? It’s not like submarines have sunroofs you could open to see what’s happening up above.

Submarines feature a special device called a periscope that allows people inside the submarine to see what’s going on above water. The word “periscope” comes from the Greek words peri and scopus, which mean “around” and “look.”

Periscopes can be used in many ways beyond seeing above water from a submarine. Periscopes were used in World War I to see beyond the tops of trenches. They’re also used frequently in armored vehicles, such as tanks, to see outside when all the vehicle’s openings are shut tight.

Periscopes are similar to telescopes in how they’re built and how they work. The main part of a periscope is a long tube that has a mirror at each end. The mirrors are attached so that they are parallel to each other at a 45-degree angle.

Arranged in this way, the mirrors bounce reflections of light between them. For example, light bounces off the object you’re looking at with the periscope. That light enters the periscope and bounces off the top mirror. The light then hits the bottom mirror and bounces into your eyes.

Isn’t it cool how a periscope uses simple scientific principles to let you see around corners or even above water from a submarine? Since submarines often can’t come all the way to the surface of the water, their periscopes have special magnifying lenses that make the reflected images bigger, so that you can see them easier.

Historians haven’t been able to pinpoint exactly who invented the periscope and when. However, they do know that Johann Gutenberg created a periscope-like device in the 1430s that allowed spectators to see over other people in a crowd at religious festivals.

Today, submarine periscopes feature all sorts of new technology to replace simple mirrors. Some use complex prisms that are much sturdier than regular mirrors. Some newer submarines don’t even have periscopes any more. They use special electronic sensors that can be raised above water. These sensors then send electronic signals back to special computers inside the submarine!

18 Join the Discussion

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    • Hi there, Jack! We think it’s GREAT that you’re the very first Wonder Friend to check out all the WONDERful facts about submarines in today’s Wonder of the Day®! Thanks for sharing something extra you know about submarines, too! Have a GREAT day! :-)

  1. This was a fun one. However, I already knew how they saw above water. I remember making periscopes out of milk cartons and mirrors. It was fun. Thanks a lot!!

    • We think it ROCKS that you already had some background knowledge about submarines before you explored today’s Wonder, boyWONDER! It’s SUPER cool that you’ve already made periscopes out of milk cartons and mirrors before, too…THANKS for sharing that! :-)

  2. I was very close to guess today’s wonder. :) I loved today’s wonder! :D I think tomorrow’s wonder of the day is about worms.


  3. Hi,

    We are still wondering why the periscope in the video has lines on it to divide the circle into fourths??????
    We think it is pretty cool that periscopes are changing into computer technology.
    Some of us thought it was a telescope instead of a periscope.
    How is oxygen provided inside of the submarine? How does it stay fresh?
    Thanks for the links to make a periscope. Some of us might make one. Mrs. G’s class

    • We’re so glad to hear from you today, Mrs. G’s class! It makes us SUPER happy to learn that you guys are doing more WONDERing about periscopes after exploring today’s Wonder together!

      We did some more WONDERing and discovered that the lines on some periscopes help the person looking through the periscope determine the distance between the submarine and objects in the distance. We also learned that some newer periscopes have night vision and other cool technologies in addition to video and magnification capabilities.

      Even though submarines can get air through hatches and tubes when they are at the surface of the water, it’s not that easy when they are below the surface. Submarines are equipped with special machines that produce oxygen and constantly monitor and clean the air when they are deep underwater.

      Thanks for WONDERing with us today! We’re glad you guys are Wonder Friends! :-)

    • That’s a really great guess for tomorrow’s Wonder of the Day®, WonderGirl! We like it a lot! Thanks for visiting Wonderopolis today and leaving us a super cool comment! :-)

    • Howdy, Rahul! We’re so super glad to hear from you today! Thanks for sharing what you think tomorrow’s Wonder will be about…we like your guesses! :-)

    • Your comment makes our day, Carlos! We think it ROCKS that you are inspired to create new things and WONDER about the world around you! Thank you for letting us know…and THANK YOU for visiting Wonderopolis today! :-)

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Have you ever wondered…

  • How does a submarine see above water?
  • What is a periscope?
  • Can you make your own periscope?

Wonder Gallery

Try It Out

Ready to make your own periscope? You can use it when swimming or for spying around corners! There are several different ways you can make a homemade periscope. Some are simple, and some are more difficult.

Check out the links below and choose a project that suits your needs based upon the time and materials you have available:

When you’re finished, let all your Wonder Friends know how your periscope works! Post a picture on Facebook and let everyone know how much fun you had making your own homemade periscope. We can’t wait to see what you make!

Still Wondering

In National Geographic Xpeditions’ Submarines: The Classroom Fleet lesson, children study the submarine and the challenges humans face when traveling underwater.

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Wonder What’s Next?

Tomorrow’s Wonder of the Day stars one of the most unique mammals you’re ever likely to meet!

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