Before the war, people mainly used ships and boats, therefore, the people with the submarine could destroy these ships.
Submarines changed war. They played a big part of World War I and II.
Commerce warfare (Guerre de Course).
World War 1 introduced aerial warfare with airplanes and trench warfare
It sounds as if you are looking for submarines.
There were subs in the 19th century, but they were really a part of naval warfare from World War One to the end of the Cold War. If large scale war breaks out in the near future, expect submarines to be a huge factor on the ocean front.
Submarines, particularly German U-boats, had a significant impact on World War I by disrupting Allied shipping and trade routes. Their ability to launch surprise attacks on naval and merchant vessels challenged traditional naval warfare and led to severe losses for the Allies. This unrestricted submarine warfare contributed to the United States entering the war in 1917 after several American ships were sunk. Ultimately, submarines changed naval strategy and highlighted the importance of underwater warfare in modern conflicts.
Why don't you just Google "World War 1 Submarines?"
Yes, submarines were used in World War I, primarily by Germany, which employed U-boats (Unterseeboote) to disrupt Allied shipping and trade routes. The use of unrestricted submarine warfare aimed to blockade Britain and cut off supplies. This tactic significantly impacted naval warfare and contributed to the eventual entry of the United States into the war. Other nations, including Britain and France, also utilized submarines, though to a lesser extent.
they used trench warfare and used powerful machineguns
trench was the most common but there was also airfighting and underwater in submarines ( then known as u boats)
World War I submarines were primarily used to locate and attack surface cargo and warships.
The nickname of German submarines during World War I was "U-boats," which stands for "Unterseeboot," meaning "undersea boat" in German. These submarines played a significant role in naval warfare, employing tactics such as unrestricted submarine warfare to disrupt Allied shipping. U-boats became notorious for their effectiveness in sinking merchant and military vessels. The term has since become synonymous with German submarines in both World Wars.