President Bush offered a nation's gratitude Monday to the families of 47 sailors killed aboard the USS Iowa, saying they were "America's pride who died for the cause of peace and freedom."

At a memorial service in the Iowa's home port, Bush pledged to more than 3,000 people in a cavernous aircraft hangar that an investigation will find the reason for the explosion in the battleship's No. 2 turret during routine maneuvers last week."I understand your grief," said Bush, a naval aviator in World War II. "I, too, have stared at the empty bunks of lost shipmates and asked, `Why?' I promise you today we will find out why - the circumstances of the tragedy.

"To all who mourn a son, a brother, a husband, a father, a friend, I can only offer you the gratitude of a nation, for your loved one served his country with distinction and honor."

The president spoke at a podium backed by a huge American flag and fronted by 47 symbolic roses. The 30-minute service included mournful processionals by the Atlantic Fleet band and words of prayer from Navy officials before Bush and his wife, Barbara, moved down a line of grieving relatives grasping hands.

The Navy said 371 relatives of the victims attended the non-denominational service, including 181 wives, children, parents or siblings.

Bush told the widows, "You have always been strong for the sake of love. You must be heroically strong now. As for the children of the lost, throughout your lives you must never forget your father was America's pride.

"This world is a more peaceful place because of the USS Iowa," he said. "So never forget that your friends died for the cause of peace and freedom."

Capt. Fred Moosally, the Iowa's commander, said no sailor continuing aboard the vessel will forget the dead either. He told the crowd, "I remember Turret 2. They were the life, the spirit and the soul of our ship. They embodied the ideals of our history and the hope of a brighter tomorrow."

After the Bushes left the base, Moosally answered questions at a news conference along with a blast survivor, gunner's mate third class Kendall Truitt, and members of the ship's firefighting crew. That was to be followed by tours of the Iowa, although not the damaged turret. Like police at a crime scene, the Navy wants no evidence disturbed until its inquiry is complete.

The investigation is being led by Rear Adm. Richard Milligan, commander of a destroyer group in Charleston, S.C. Milligan and his six-officer team were on the Iowa as it made its way from Puerto Rico, to its Sunday arrival in Norfolk.

As tugboats nudged the 887-foot ship to shore, a roar swelled from the sign-waving crowd of roughly 2,500 that met it. Sailors manning the rails stood at attention in dress white uniforms with black mourning arm bands.

As the Iowa slid into Pier 5 at the world's largest naval base, observers could see no "bloomers" outside turret No. 2's gun barrels, which jutted up and to the right in testimony to Wednesday's accident. Cmdr. John Woodhouse explained that the covers to keep out moisture were blown away in the blast.

The 17-inch turret armor designed to protect sailors from outside harm contained the blast inside and turned the 5-story complex into a steel tomb.

The accident occurred 330 miles northeast of Puerto Rico during routine 2nd Fleet exercises. The maneuvers are continuing; Vice Adm. Jerome Johnson transferred his flag from the Iowa to the cruiser USS Thomas Gates to oversee the exercises until their May 4 completion date.