What to know about Coast Guard Island in California, where federal agents have headed

Federal immigration agents were greeted by protests Thursday in the San Francisco Bay Area on their way out to a century-old, government-owned artificial island that houses a U.S. Coast Guard base.

U.S. Customs and Border Protection agents began arriving at Coast Guard Island to support federal efforts to track down immigrants in the country illegally. The Coast Guard is part of the U.S. Department of Homeland Security, along with Customs and Border Protection, and Immigration and Customs Enforcement, or ICE.

A statement provided to the news media by the Coast Guard said that “through a whole of government approach, we are leveraging our unique authorities and capabilities to detect, deter, and interdict illegal aliens, narco-terrorists, and individuals intent on terrorism or other hostile activity before they reach our border.”

President Donald Trump then said Thursday that he’s backing off a planned surge of federal agents into San Francisco after speaking to the mayor. It was not clear if the president was canceling a National Guard deployment or calling off immigration enforcement by CBP agents.

Coast Guard Island is a 67-acre manmade island formed in 1913 in the Oakland Estuary between Oakland and Alameda. It is federally owned, does not allow visitors from the general public without an escort or specific government identification, and has been home to the current base, Base Alameda, since 2012, according to a Coast Guard document from 2016.

Base Alameda provides a variety of services for Coast Guard activities throughout the West Coast.

The island was built partly to deal with sanitation problems in Alameda through an 1873 proposed tidal canal. By 1918, the island built using reclaimed mud from dredging was ready to be occupied. Its first tenant was the San Francisco Shipbuilding Company, which made two ships before closing in 1921.

The Coast Guard first came to the island in 1926 when it established a base there. The Coast Guard used the land for various purposes, including a training center set up in the 1940s and closed in 1982. That year, the Coast Guard established Support Center Alameda and the island was renamed Coast Guard Island.

Ultimately, in February 2012, the Coast Guard set up Base Alameda on the island, combining several existing operations to set up departments in the base.

According to the 2016 Coast Guard document, Coast Guard Island employs more than 1,200 people during the workday, including active duty military, Coast Guard Reserve, civilians, contractors and occasional Guard Auxiliary personnel.

The island has a perimeter of about 1.25 miles.

The base is the home port for four so-called national security cutters — ships that are 418 feet long, 54 feet wide, with a top speed over 28 knots, a range of 12,000 nautical miles, endurance up to 90 days, and capacity for a crew of up to 170, according to the Coast Guard.

One of them just recently returned from an Arctic deployment of more than 21,000 nautical miles.