SHICHIGAHAMAMACHI, Japan — A line of somber soldiers walked methodically through a drained swamp Monday, with each step sinking their slender poles into the muck beneath.

If one hit a body, he would know.

"Bodies feel very distinctive," said Michihiro Ose, a spokesman for the Japanese army's 22nd infantry regiment.

The men were among 25,000 troops given the morbid duty of searching the rubble, the seas and the swamps of northeastern Japan for the bodies of the nearly 12,000 people still missing in last month's earthquake and tsunami.

The two-day operation was the biggest military search since the March 11 disaster. With waters receding, officials hoped the troops, backed by police, coast guard and U.S. forces, would make significant progress. By Monday evening, they had found 38 bodies, the military said.

In the town of Shichigahamamachi, about two dozen Japanese soldiers in black boots, white masks and waterproof jumpsuits traveled silently in unison across the soggy earth, made even softer by torrential rains an hour earlier. In some areas, the mud came up to their knees.

The search focused on a long, narrow marsh drained in recent weeks by the army using special pump trucks.