The second island chain extends from Yokosuka in Japan, through Guam, then through Palau to Papua New Guinea. The defensive theory was espoused by former diplomat and Republican John Foster Dulles, Secretary of State during the Korean war as a means to contain the Soviet Union and China strategically. 

Really, the second island chain is all about Guam, unlike the first island chain, there is plenty of blue water between the islands and the island does not disrupt shipping like the first island chain. With Palau now included in calculations, the prospect of further logistics assets in the region enhances both defensive and offensive prowess. I am betting on a radar installation as Palau is east of Mindanao and south west of Guam 

The US gained the territory in 1898 after victory in the Spanish – American war. The US has maintained an air base on Guam since late world war two after establishing a B-29 airfield to conduct raids on Japanese positions on their way to defeat Japan. The naval base was overrun and lost not long after the Pearl Harbor surprise attack in the second world war before being retaken by the US Marine Corps in 1944. 

.The air base was upgraded during the Korean War with B-36, replaced by B-47 bombers stationed there during that conflict. Anderson air base was active during the Vietnam war, B-52 bombers flew missions from the base after replacing the B-47 bomber fleet in 1964. Anderson was an important base throughout the cold war, the B-52 fleet was an integral facet of the US nuclear deterrence.

As a logistics base, Naval Base Guam and Apra Harbour supports naval assets with a deepwater anchorage and repair facilities. The naval base is an important asset in the western Pacific, a small contingent of marines operate from the base along with the army that shares facilities. The US Army operates defensive missile systems on the island, 

The small island nation of Palau figures largely in US strategy, the site of fierce fighting, there are still Japanese aircraft and shipping wrecks scattered around the islands. Should the US and allies be denied access to the first island chain by China, or even be expelled from the region in the case of all out war. The second island chain is not necessarily defensive, this may be the forward operating bases. 

I am intrigued to learn what is planned for Palau, radar is pretty much absolute, I am wondering if naval logistics is planned, if the US Army is going to operate missile defence systems or maybe an offensive missile system is planned. They may be planning anti-ship missile batteries due to the location between the Philippines, Papua New Guinea and Guam – this is a less strategic location, but I am guessing a secondary support base.