Emperor Akihito and Empress Michiko visited a memorial near Tokyo on Monday that commemorates 60,000 civilian sailors who were commandeered by the Imperial Japanese Army and died while transporting military supplies and personnel during World War II.

The emperor, who will abdicate in April, and his wife prayed for peace and offered a bouquet of white chrysanthemums at the monument in the city of Yokosuka in Kanagawa Prefecture.

During the war, most civilian vessels were requisitioned by the Japanese military and their crews were forced to transport weapons or conduct maritime surveillance. Few battleships were available to defend them, leaving them vulnerable to attacks by the Allied forces.

More than 2,000 ships were destroyed and 60,000 people were killed, according to the government and a Tokyo-based foundation honoring sailors who died in the line of duty.

Around 30 percent of the victims were in their teens, they said.

It was the imperial couple's eighth visit to the memorial. They first visited it in May 1971, two months after it was erected.

The emperor recalled the victims at a press conference ahead of his birthday in December 2015, saying, "In those days, Japan lacked command of the air and no battleships were available to escort the transport vessels. It gives me great pain to think of the feelings of those sailors who were forced to engage in such transport operations under those conditions."