In celebration of the Mid-Autumn Festival, equip the ship of your choice with the Mosaic permanent camouflage. Unlock the DLC for free, then play 10 battles to claim it. Enjoy, Captain!
This limited-time exclusive DLC is only available from September 14 through October 1, 2024, and can only be unlocked with a World of Warships game account that was created through Steam.
Seems more like they're (ab)using Steam to do advertisements again? (Or open you up to further advertisements)
For reference, they spammed anyone with the free license to the game with advertisement box items, and Valve got enough complaints that they went and locked down the Inventory API to prevent this. (Now they're only allowed to send items to people who have playtime in the last 30 days)