The chairman of the Joint Chiefs of Staff on Wednesday said he has spoken to his Russian counterpart three times to warn against provocations that could lead to U.S. retaliation such as the "attack profile" flybys by Russian warplanes of the guided missile destroyer USS Donald Cook this month. In testimony to the Senate Appropriations Defense Subcommittee, Marine Gen. Joseph Dunford said that he initiated the phone conversation with Gen. Valery Gerasimov, chief of the General Staff of the Armed Forces of Russia, and "I've now spoken with him three times." Dunford said that he and Gerasimov agreed not to discuss the substance of their talks but he had "conveyed the message that you'd expect us to convey." Responding to questions from Sen. Susan Collins, a Maine Republican, and Sen. Dick Durbin, an Illinois Democrat, Dunford said that the flybys pose "a risk of miscalculation arguably greater than it was in the Cold War." Collins said she was concerned that the Russians were "engaging in behavior that eventually is going to lead to military engagement." Durbin said he had spoken to Russian Ambassador Sergey I. Kislyak and the ambassador "almost laughs me off" and asks "why do you keep bringing this up?" Kislyak said the Russian warplanes were "perfectly within their rights" in the flybys of the Cook, Durbin said. However, Dunford said Cmdr. Charles E. Hampton, commander of the Cook, as well as the commanders of all U.S. ships, "has a responsibility to defend that ship. He doesn't have to ask anybody up the chain of command "for permission to defend his ship and its crew." The flybys put "that commanding officer in a situation where he has to make a judgment call" and "it absolutely establishes the risk of miscalculation," Dunford said. As the Cook left the Polish port of Gdynia on April 11, and was about 70 miles from the Russian enclave of Kaliningrad in the Baltic Sea, two Russian SU-24 jets made about 20 passes of the ship, some of them at an altitude estimated at just 100 feet. In the second incident on April 12, two Russian KA27 Helix helicopters flew several circles around the Donald Cook, apparently taking photos, after which two jets again made numerous close passes of the ship in what the Pentagon later described as a "Simulated Attack Profile." Gerasimov is the author of what analysts now describe as the "Gerasimov doctrine," which is seen as the template for the "hybrid warfare' carried out by Russia in the takeover of the Crimea and in support of the separatists in eastern Ukraine. In a paper published in 2013, Gerasimov said that the purpose of modern war was to erode the "readiness, will and values" of the enemy through "non-military means."--Richard Sisk can be reached at Richard.Sisk@Military.com.