They weren’t manned by robots

“The last surviving ship of a 21-vessel Japanese convoy was sunk off Singapore. The tanker Sarawak Maru ended up like the others, picked off one-by-one over a ten-week period as the convoy attempted to bring supplies from Japan to forces in southeast Asia. Some were sunk in daylight attacks by carrier planes and in nighttime attacks by submarines in the China seas; others were hit by mines strewn along their path in the Singapore Strait; eventually all were lost.” – Robert Goralski, “March 19, 1945,” World War II Almanac: 1931-1945