An Army rapid deployment force will practice securing the Pentagon’s strategic missile defenses base in Alaska this week as part of annual exercises involving both conventional and nuclear forces.

Defense officials said an Army Quick Reaction Force (QRF) of 55 airborne troops, along with weapons and vehicles, will parachute into Fort Greely, Alaska, on Thursday as part of exercises called Vigilant Shield.

The QRF, made up of highly-trained, extremely mobile forces, will quickly unpack vehicles and arms and move to set up a security perimeter around the Ground-Based Interceptor (GBI) field at the base—all within minutes of hitting the ground, said officials familiar with some details of the exercise. The exercises will continue through Oct. 28.

The Pentagon has deployed 26 long-range interceptors at Fort Greely and four at Vandenberg Air Force Base, California. The interceptors are a key element of the military’s limited U.S. strategic defenses against long-range missile attacks, anticipated principally from North Korea.

Military spokesman declined to reveal the scenarios for the exercises citing "operational security" fears.

The U.S. military exercises, however, follow a large-scale increase in Russian strategic nuclear bomber flights near both Alaska and California.

And the war games, involving deployment of hundreds of Canadian troops, are also being held as Russia announced last month it is reopening a Soviet-era naval base in the Arctic far-northern New Siberian Islands. Six Russian warships, including two landing ships, departed for the island with troops and supplies on Sept. 6.

The Siberian island base is about 1,000 miles from the Alaskan coast and is part of a major push by Moscow to build up its military forces throughout in the resource-rich Arctic region.

Retired Air Force Lt. Gen. Thomas McInerney, a former Alaskan Air Command commander, said the U.S. exercises are not limited to missile defenses and appear to be a response to recent large-scale Russian nuclear exercises and bomber activity.

"Northcom is exercising its forces to demonstrate its ability to defend not only our GBI Missile site but to also show that the Alaskan Command has force projection capabilities to operate anywhere in the Alaskan NORAD Region to defend important nuclear warning sites in the Aleutian Island chain, as well as mainland Alaska," McInerney said.

"This clearly is in response to the extensive Russian nuclear exercises that have been conducted recently and is a welcome sign that this administration has not completely disarmed our nuclear deterrent readiness," he added.

Defense Secretary Chuck Hagel in November outlined a new Pentagon strategy for securing the arctic. The strategy followed increased Russian and Chinese inroads in the region. Hagel said in a speech Nov. 22 that melting polar ice had increased sea routes and as a result there is an increased the risk of a future conflict in the region.

Russia has targeted U.S. missile defenses in the past.

In February 2013 a Russian Tu-22M Backfire bomber made simulated air-launched cruise missiles firings at an Aegis ship deployed near Japan that is part of regional U.S. missile defenses, U.S. officials said.

Earlier, the Russians made a more direct threat against the U.S. missile defense facility at Fort Greely during large-scale nuclear exercises in June 2012.

The exercises involved 30 Tu-95 Bear bombers and Tu-160 Blackjack bombers near Alaska.

At the time, Russian Air Force Lt. Col. Vladimir Deryabin, a Defense Ministry spokesman, was quoted in state-controlled news media as saying the mission of the exercise was to "practice destruction of enemy air defenses and strategic facilities."

Defense officials familiar with intelligence reports said the bomber exercises highlighted Russia’s targeting of missile defenses at Fort Greely, as well as practice attacks on the U.S. oil pipeline in Alaska that delivers 11 percent of U.S. oil.

Classified State Department documents made public by Wikileaks revealed several years ago that Russian offensive military exercises in the arctic are part of an effort by Moscow to "emerge as the dominant arctic power."

In addition to the Siberian islands base, Russia’s military is opening arctic air bases in the far north at Naryan-Mar, on Novaya Zemlya, and Franz Josef Land.

Russia also has announced it is creating an Arctic Brigade of 8,000 troops to be deployed on the Kola Peninsula near Finland and Norway.

Securing the missile defense interceptor field is one of the field elements of large-scale war games taking place this week. The airdrop is part of Vigilant Shield, an annual homeland defense exercise run by the Colorado-based U.S. Northern Command and the U.S.-Canada North American Aerospace Defense Command.

The field exercises at Fort Greely initially were to involve an airdrop of 400 airborne troops to from the 4th Brigade of the 25th Infantry Division based at Fort Richardson, Alaska. The exercise was scaled back to just the QRF, however.

Air Force Capt. Matthew Miller, a Stratcom spokesman, said the two exercises are linked through scenarios designed to provide the best training. Information on actual scenarios and operations is classified, he said.

Some 550 Canadian military troops and 20 aircraft will also take part in the war game by deploying to Goose Bay, Labrador, in northeastern Canada in what Northcom said will be the first major deployment for Norad in over a decade.

Norad’s main mission is to prevent air attacks on North America.

Canada’s government recently has voiced concerns about Russian strategic bomber incursions.

The Washington Free Beacon reported Sept. 8 that Russian strategic bombers conducted practical nuclear cruise missile attacks from areas near northeast Canada.

Concurrently with Vigilant Shield, the U.S. Strategic Command on Monday launched large-scale nuclear war games called Global Thunder designed primarily to test nuclear command and control, along with other command military operations involving space, cyberspace, missile defense, combating weapons of mass destruction, and intelligence, surveillance and reconnaissance, the command said in a statement.

The Stratcom war games will be simulations and field exercises at various locations. The exercise is based on a fictional scenario and is not related to real world events, the command said in a statement.

All command mission elements will take part in the exercise including task forces, missile and submarine units, command posts, and bomber wings.

Adm. Cecil D. Haney, Stratcom commander, recently expressed concern about large-scale Russian nuclear forces exercises in Europe that were held after Moscow’s military annexation of Ukraine’s Crimea. He also expressed worries over the closeness to the United States of recent Russian nuclear bomber incursions into U.S. air defense zones.

"This exercise, and our continued focus on maintaining key capabilities and skills, ensures U.S. Stratcom’s strategic forces remain relevant and ready, 24/7, providing flexible and credible options for the president and the Department of Defense," Haney said in the command release.