What installations are on Guam and how significant are they?
Guam has two major bases: Andersen Air Force Base in the north and Naval Base Guam in the south.
The naval base dates to 1898, when the US took over Guam from Spain after the Spanish-American War. The air base was built in 1944, when the US was preparing to send bombers to Japan during World War II.
Today, Naval Base Guam is the home port for four nuclear-powered fast attack submarines and two submarine tenders.
Anderson Air Force Base hosts a navy helicopter squadron and air force bombers that rotate to Guam from the US mainland.
Altogether, 7000 US military personnel are stationed on Guam. The military plans to move thousands of US Marines to Guam from Okinawa in southern Japan.
Guam's total population is 160,000.
What roles do the bases play in the region?
Guam is strategically located a short flight from the Korean Peninsula and other potential flashpoints in East Asia. Seoul is 3200km to the northwest, Tokyo is 2400km north and Taipei is 2700km west.
The naval base is an important outpost for US fast-attack submarines that are a key means for gathering intelligence in the region.
A satellite image of the island of Guam acquired by NASA's Earth Observing-1 (EO-1) satellite. Source: AAP/NASA Earth Observatory
How has the US used Guam to address the threat from North Korea?
The US military began rotating bombers - the B-2 stealth bomber as well as the B-1 and B-52 - to Andersen in 2004.
In 2013, the army sent a missile defence system to Guam called Terminal High Altitude Area Defense, or THAAD.
What's the history of the US military on Guam?
The US took control of Guam in 1898, when Spanish authorities surrendered to the US Navy. It used the island as a coaling base and communications station until Japan seized the island in 1941. The US took back control in 1944.
During the Vietnam War, the Air Force sent 155 B-52 bombers to Andersen to hit targets in Southeast Asia. Guam was also a refuelling and transfer spot for military personnel heading to Southeast Asia. Many refugees fleeing Vietnam were evacuated through Guam.
