About 130 U.S. soldiers are returning to their bases after being deployed last week to a remote western Alaska island with mobile rocket launchers amid a spike in Russian military activity off the western reaches of the U.S., a military official said Thursday.

The deployment to Shemya Island involved soldiers from Alaska, Washington and Hawaii with the 11th Airborne Division and the 1st and 3rd Multi Domain Task Forces, Sgt. 1st Class Michael Sword, a spokesperson for the 11th Airborne, said in an email to The Associated Press.

The deployment coincided with eight Russian military planes and four navy vessels, including two submarines, traveling close to Alaska as Russia and China conducted joint military drills. None of the planes breached U.S. airspace.

A Pentagon spokesperson said earlier this week there was no cause for alarm.

Maj. Gen. Joseph Hilbert, commanding general of the 11th Airborne Division, has told media the deployment to the island 1,200 miles (1,931 kilometers) southwest of Anchorage was done at the right time.

The deployment occurred Sept. 12. The North American Aerospace Defense Command said it detected and tracked Russian military planes operating off Alaska over a four-day span. There were two planes each on Sept. 11, Sept. 13, Sept. 14 and Sept. 15.

The exercise was a measure of the military's readiness to deploy troops and equipment, Sword said.

“It’s a great opportunity to test ourselves in real-world conditions, and another benefit to being stationed in a place like Alaska,” Sword said.