ROMA, Tex. — From a compact, portable shed on the outskirts of this border town, Jonathan Hoyt has an expansive field of vision. His computer is linked to cameras and surveillance equipment that allow him to see rubber rafts on the Mexican side of the Rio Grande nearly three miles away, simply by moving a tiny joystick.

Mr. Hoyt, a Border Patrol agent, is using equipment that the Defense Department brought back from Afghanistan, where it was used to track the Taliban. It is part of a potent arsenal that also includes towers, drones and aerostats — giant blimps attached to the ground that can hover as high as 5,000 feet. Helicopters using powerful infrared sensors and video cameras also patrol the skies.

Law enforcement officials say that deploying this array of technology has resulted in tens of thousands of arrests on a border that remains a primary transit point for drug smuggling and migrants crossing into the country illegally.