https://www.pcgamer.com/world-tier-5-tidal-basin-release-date/

In a livestream for The Division 2, the team confirmed the imminent arrival of the Tidal Basin stronghold, opening the door to World Tier 5 for those who have hit the endgame. The Invasion: Battle for D.C. should flesh out the game further for level 30 players, including new mission invasions, the first gear sets and a new heroic difficulty setting. It's coming on April 5. 

Tidal Basin is a high-tech military base—think Shadow Moses—full of heavily armed troops waiting for you and your mates. It's a big one, we're warned, but completing it will bump you up to World Tier 5, giving you access to a bunch of new challenges and appropriate rewards. You'll also net yourself one of the first three gear sets: True Patriot, Hardwired and Ongoing Directive.