Asian nations in Laos.

Germany is increasing its military presence in the Indo-Pacific region.

It has joined naval exercises with Japan, the US and other allies.

One aim is to keep trade routes open.

Our reporter Georg Mattes has been on board the German frigate Baden-Württemberg.

At a brisk speed of 25 knots, the German warship crosses the invisible sea border.

It's now out of Indonesian waters into what's called the high seas.

The digital map signals the crew of the frigate Baden-Württemberg that they can now start their training manoeuvre.

Today we have flight operations, so we first have to cross the territorial waters from

Indonesia to the high sea before we can launch our helicopter.

Whether you're on the high seas or whether you're within so-called exclusive economic or territorial waters is complex and often a matter of interpretation.

Just as in the case of the South China Sea, which the Baden-Württemberg recently crossed.

China claims sovereignty over about 90 percent of it.

Which contradicts the UN Convention on the Law of the Sea, says the maritime legal expert on board.

China used this to interpret it, to bring their own interest in the interpretation of the law of the seas.

And that is not only China, all coastal states, all states that bring ships into the sea interpretate and set their own interests in this law.

This is a fact.

About a third of global maritime trade passes through the South China Sea annually, making unhindered passage essential to the global economy.

Germany's deployment in the region was a signal that all nations should be able to manoeuvre freely in international waters, including Singapore, which today is also participating in the military exercise.

While sailing through the South China Sea, the German warship was shadowed by Chinese vessels, sticking to the same route and maintaining about the same distance as this warship from

Singapore.

The German fleet admiral explains that shadowing other ships is routine and that during the

Baden-Württemberg's transit through the South China Sea, the Chinese kept an appropriate distance.

The fact that China was closely observing Germany's passage through waters they claim for themselves was very much part of the mission.

As we recognise the Taiwan Strait as well as the South and East China Sea as international waters and the high seas, we acted in accordance with international maritime law and exercised the freedom of navigation and the freedom of being in international waters and at the high seas.

The German Indo-Pacific deployment was the second mission of its kind.

Germany plans to return soon to show allies in the region that when it comes to upholding the freedom of navigation, they are ready to sail alongside them.