Why are they doing this? Well, as China strengthens its air defenses, the Navy thinks that launching these hypersonic missiles from submarines will be more effective than from land or surface ships. They believe it'll help them penetrate China's defenses and take out important targets like control centers.

These hypersonic missiles fly really fast - about five times the speed of sound - and they're designed to hit targets thousands of kilometers away in just 15 to 30 minutes.

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First, these missiles will be given to the Army, then to the Navy. Initially, they'll be installed on some special destroyers called Zumwalt-class destroyers in the mid-2020s, and later on a type of submarine called Block V Virginia-class submarines in the early 2030s.

To make sure these missiles work underwater, the Navy is building a testing area at a place called the Naval Surface Warfare Center in Crane, Indiana. This testing area will help them understand how the missiles move through the water.

Launching these missiles from a submarine is tricky. They have to be pushed out of a tube using high-pressure gas before the booster kicks in and they start flying. This is different from how missiles are usually launched, where they ignite and fly out by themselves.

Experts say that using submarines for these missiles is really important because submarines can move quietly and sneakily, especially close to enemy shores.

Meanwhile, China and Russia are also working on their own hypersonic missiles. But according to a senior intelligence analyst, China is ahead of Russia in terms of how many hypersonic missiles they have and how they're using them.

Overall, these hypersonic missiles could be a big deal in future military operations, but some experts question whether they're worth the high cost and if they're really that much better than other types of missiles.