Difference between the US army, navy, and air force.

In the USA, there are 3 main military forces. The army, the navy, and the air force. The army fights mostly on land. The navy fights on water. And the air force fights in the air.

These 3 main military forces are divided into several parts. One of these parts is the infantry. The infantrys role is to fight the enemy. The army and the navy both have infantries. The army infantry is called the infantry. In the navy, it is called the naval infantry or the marines.

At first, the marines role was to provide security on ships, to board other ships, and to repel boarding. Sometimes the marines would help with land raids. But now they are doing more water missions.

The US Marines Corps is a very large infantry. The US has used the marines for things other than a landing force for a naval invasion, but an expeditionary force, going in before other forces, even in places far from the sea.