ANTWERP, Belgium (AP) — Britain may have just left the European Union, but the country’s navy was the first to arrive for U.S.-led war games over the next six months across Europe.

The Royal Navy was busy Monday offloading heavy military vehicles in the Belgian port of Antwerp. The vehicles will be involved in the Defender-Europe 2020 exercises, which will see the biggest deployment of U.S. troops — some 20,000 personnel — to Europe in the last 25 years. In all, around 37,000 soldiers from 18 countries, not all of whom are members of the NATO military alliance, will be taking part.

The war games are a test of the U.S. military’s ability to pour thousands of troops and equipment into Europe alongside NATO allies and partners in times of crisis. Many of the exercises will be held in countries neighboring Russia like Poland, Estonia, Latvia and Lithuania.

The bulk of the forces are deploying in February, with the main exercises taking place in April and May. The maneuvers wind up in August. Some of the exercises will involve air-dropping soldiers to pre-positioned equipment or erecting temporary bridges for river crossings in combat-like conditions.