What happened?
China conducted its first orbital sea launch on 5 June 2019, with a Long March 11 rocket lifting off from a floating platform in the Yellow Sea off the eastern province of Shandong. The launch was a four-stage solid-fuelled rocket which carried seven satellites into orbit, five commercial satellites, along with two experimental satellites to improve weather forecasting. The launch was named ‘LM-11 WEY’ after a strategic partnership between WEY, a premium SUV marque of Great Wall Motor China Space Foundation and China Academy of Launch Vehicle Technology (CALT) who together founded a joint technology innovation hub on April 24, 2019, this is said to help the SUV maker achieve a number of newer innovations in R&D and manufacturing areas.

What is the background?
China has joined the US and Russia who also have the capability to launch rockets from the sea. It was the 306th flight for the China National Space Administration's line of Long March carrier rockets, but the first time one has taken off away from solid ground, making this a significant milestone for China’s ambitious space programme. 

This launch also followed the historic mission of the China National Space Administration land of a probe on the far side of the Moon in January 2019 a mission that had never been achieved before.

What does it mean?
There are a number of reasons why the ability to launch rockets from the sea rather than land is more advantageous. It allows for boosters which can lift off from closer to the equator, which in turn will give greater speed and in turn greater payload capacity. Therefore, it requires less energy to reach space which means fuel savings, while the dangers posed by falling debris are also less than otherwise be.
China is also building up its naval capacity through launches like this. They have also entered into a probable space war with the US and Russia in it.