If you remember anything about World War 1 from your high school history class, it's probably something about maps, complicated borders and people fighting. But animals played a big part in the conflict too.

Around the world more than 65 million people served in the war, but there were also more than 16 million animals helping them do their job. Animals did everything people did during the war. They were soldiers, spies and messengers, they helped heal wounded troops and kept the trenches supported.

They were also pets, mascots and friends who supported these young men when they needed help the most. These vintage photos show just how important animals were during this huge part of our history.

The most important kind of animals during the war were pack animals like horses and donkeys.

This was a time when cars and trucks were still pretty new, so these animals were important for moving troops and supplies.

And with all the horses and donkeys busy fighting the war, other animals like dogs would help do their job at home.

And of course, safety was important for dogs and horses near the front lines, so they often wore special gas masks.

Dogs were very popular animals in the war, both for support and to do quick, important jobs like delivering messages.

This is Sergeant Stubby. That's not just a cute nickname, he was an American army dog who was actually promoted for his good work. Stubby could smell gas and warn soldiers, track down injured men, and even caught a German spy!

This dog helped carry medical supplies.

While this one delivered messages. In this photo you can see he's pulling electrical wire from one location to another.

Check the next page for more vintage animal photos!

While nowadays we use vehicles in place of animals, there are still some brave K9 dogs and military animals working to keep us safe.

But while there's not shortage of animal heroes, not all of them were put in danger during WW1.

Some dogs were just mascots for the soldiers, or good company during these hard times.

This dog is actually carrying another working animal: pigeons.

These trained birds would carry messages to soldiers, and some even took pictures using special spy cameras.

There were lots of other unusual animals in the war, like this koala who was a mascot for some Australian soldiers.

This kitten who lived on a Navy ship.

And even this zoo elephant who helped move tree trunks in Germany.

In some places, soldiers even rode camels instead of horses.

And soldiers could always count on their animal friends for support.

Even pets back at home were willing to lend a hand. These dogs used their costumes to raise money for the war effort.

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