Soldiers affiliated with an army unit under the South Korean military's Special Warfare Command singing a martial song in unison after entering a reservoir by breaking the ice on its surface, in Hongcheon, South Korea, yesterday.

The day is known as daehan, one of the 24 seasonal divisions of the lunar calendar that marks the arrival of the coldest day of the year.

The exercise in cold water is part of the unit's tactical drill exercises tailored to train troops for the winter's period of severe cold.

The Special Warfare Command is in charge of the army's special operations forces and its troops often work closely with their United States Army Special Forces counterparts, the Green Berets.