In a little-known part of the counter-terrorism（反恐怖主义） world, one of the most effective detection systems is a 600-pound animal that works for about 20 pounds of fish a day. Since the 1960s, the United States and a handful of other countries have trained dolphins and sea lions to detect sea mines and swimmers, to recover inert torpedoes（鱼雷）and to test objects used in Naval exercises. Program officials estimate that the sea lions in the Marine Mammal Program have recovered millions of dollars of U.S. Naval torpedoes and instrumentation dropped on the sea floor. The U.S. Navy kept its Marine Mammal Program a secret until the 1990s, and this spring CNN became one of only a handful of media outlets to see firsthand how the program works. The program has trained about 75 Pacific bottlenose dolphins, with natural biosonar (生物声纳) that tracks better than any manmade device; and 35 California sea lions, with superb underwater eyesight. Not only do these trained marine mammals track and retrieve millions of dollars in U. S. military equipment, they are also helping to save lives. The Navy won't disclose whether the dolphins and sea lions have effectively intercepted （阻拦）terrorists attempting to do harm to any U.S. facilities. "Either way, it serves as a deterrent（阻碍） effect." says Christian Harris, operations supervisor for the program. The mammals can be deployed（调动） via C-130 cargo aircraft to perform their missions anywhere in the world within 72 hours. They have been used in exercises from Alaska to Hawaii, operating in great temperature and environmental ranges. They also have the capability to operate off vessels. Dolphins most recently were deployed in the Iraq war, performing mine detection and clearance operations in the Persian Gulf to ensure safe passage for humanitarian ships delivering aid. Some of these Iraq war "veterans" are now back home, tasked with a new mission: guarding nuclear submarines in their homeports of Bremerton, Washington, and Groton, Connecticut. 小题1:The underlined word "retrieve" in Paragraph 6 can be replaced by ________.
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