Approaching from the Hawaii coast, the mosquito-shaped helicopter buzzed around the guided-missile cruiser USS Lake Erie twice before swooping toward the landing pad. The U.S. Navy crew on the deck crouched, the helmeted faces betraying more than routine concern as the aircraft, flown by a pilot who had never before alighted upon a ship, hovered just off the tarmac and then set down with a thud.

Their trepidation was prompted by three words painted in black block letters on the fuselage: United States Army.

The army, which fights on terra firma, does not usually land its helicopters on ships — the domain of the navy and the Marine Corps — but these are not usual times in the U.S. military. As the Obama administration winds down the army-centric war in Afghanistan, Pentagon leaders are seeking to place the air force, navy and marines in dominant roles to counter threats in the Asia-Pacific region, which they have deemed to be the next big national security challenge.