HUATULCO, Mexico — Mexico’s navy seized a homemade submarine carrying a drug shipment off the Pacific Coast on Wednesday and arrested its four-man crew. Similar vessels carrying cocaine have been discovered off Colombia and Central America, but navy spokesman Capt. Benjamin Mar said the seizure is a first for Mexico. The 30-foot (10-meter) makeshift submarine was detected heading north about 200 miles (322 kilometers) off the southern state of Oaxaca, Mar said. The green-topped, arrowhead-shaped vessel was intercepted when it surfaced hours later, and the crew was taken into custody without resistance.