In the heart of Norway’s countryside, the U.S. military is bolstering its arsenal of weapons with tanks, gun trucks and other armored vehicles along with hundreds of containers of equipment.

The Marine Corps is overseeing the effort, which expands the existing Marine Corps Prepositioning Program. It stashes weapons, vehicle and armor in several locations across the world, including Norway, which first signed an agreement with the United States to do so in 1981, Marine officials said.

The equipment is kept in climate-controlled caves in central Norway, giving the Marines equipment that is closer than the East Coast to use in Europe, Africa and the Middle East. Much of what stored in the caves was pulled out and sent to the Middle East ahead of the March 2003 invasion of Iraq.

It also bolsters the amount of military equipment in Norway as tensions with nearby Russia remain high. Russian President Vladimir Putin said Monday that he may send a military convoy to eastern Ukraine on a humanitarian mission, something Western officials see as a potential pretext for a Russian invasion.

Here’s an old photo of one of the caves, courtesy of the National Archives:

The planned U.S. military expansion in Norway has been under discussion since 2013, Marine officials said. That’s before Russian-backed separatists seized the Crimean peninsula in Ukraine in February, and Putin declared it to be part of Russia in March.

The Marine Corps will soon begin adding M1A1 Abrams battle tanks, armored amphibious assault vehicles that can swim from Navy ships to shore, armored Humvee gun trucks and other vehicles in Norway, Marine officials said. Doing so will “greatly increase the program’s readiness,” Marine officials said in a news release.

One source told Checkpoint that it will mark the first time that the tanks and several other kinds of vehicles will be allowed in the caves. That includes the Marine Corps’ Assault Breacher Vehicle,  a 72-ton vehicle that has a tank chassis, but has been outfitted to clear improvised explosive devices with a plow and line that can be shot 150 yards ahead of the vehicle with explosives on it.

Here it is in action in Afghanistan:

The U.S. military has  more than 700,000 square feet of facilities in Norway, including six climate-controlled caves and two airfields. The Norwegians have maintained the equipment there with the understanding that if they were invaded, U.S. troops will defend them using it.