The nation's top military officer told midshipmen at the U.S. Merchant Marine Academy in Kings Point Monday night that their work on maritime security is "vital" in an increasingly complicated world.

Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, described that work as never-ending, keeping oceans open to trade during peacetime and supporting military operations during war, including most recently with operations in the Middle East.

Dempsey has previously warned of maritime threats ranging from piracy, trafficking and terrorism to the expansion of maritime claims and restriction of movement on the oceans by nations like Russia and China in the Arctic and Pacific.

But Monday night, speaking on the 70th anniversary of the U.S. victory at Iwo Jima at the Kings Point school's Battle Standard Dinner, an annual event honoring 142 midshipmen who lost their lives during World War II, Dempsey did not dwell on current events, directing much of his address to character and personal responsibility.

"The one thing you will always control is your actions," he told midshipmen in the packed dining hall. "Take ownership of your profession from day one."

About a quarter of the academy's graduating class of 230 will go on to military service. The rest will take commissions in the Navy Reserve.

The work and sacrifices of merchant mariners have sometimes been overlooked, Dempsey said.

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Merchant mariners -- including cadets -- ferried Marines into the fight at Iwo Jima and took them off the island when they were wounded. Some were wounded themselves, he said, telling the story of a young merchant marine named Fred Carrier who took a piece of shrapnel in the elbow during the 1945 battle. "Well, hell, what do you want -- a Purple Heart or a day off?!" Carrier recalled his commanding officer saying. According to newspaper accounts, Carrier received neither.

Four academy graduates have been killed in service in recent years, and when the applause after Dempsey's remarks quieted, some of the midshipmen acknowledged they were entering a perilous world.

"It's not going to be a cakewalk," said Midshipman 1st Class Nicholas Vogel, 22, of Mechanicsburg, Pennsylvania, who is bound for the Marines and was recipient of the 1st Lt. William James Donnelly IV USMC Memorial Award, named after one of the deceased.