ALAMEDA, Calif. — Vice Adm. Fred Midgette, commander of Coast Guard operations in the Pacific Area, has a challenge almost as vast as the ocean he patrols in search of drug traffickers, with responsibilities for an area that is twice the size of the continental United States.

The Coast Guard is struggling to keep pace, seizing about 20 percent of all the drugs that come into the United States through a coastal border, as its aging fleet attempts to pursue the speedboats favored by the traffickers.

“When most people think border security, they think Border Patrol,” Admiral Midgette said. “What we do by intercepting drugs on the high seas has a direct connection to what happens at the southern border in terms of stopping illicit drugs and illegal immigration.