I want to know the answer to the following question:
What did Spain build to protect their fleet at Guam?
All the background I'm provided with is that "From 1565 to 1815, Guam and the Northern Mariana Islands, the only Spanish outpost in the Pacific Ocean east of the Philippines, was an important resting stop for the Manila galleons, a fleet that covered the Pacific trade route between Acapulco and Manila.:51". Is that enough to answer the question?