The major rescue operation on Mount Ontake—the 10,062-foot volcano that erupted in Japan last month—is now over.

It was a quick response and an example of Japanese disaster relief work at its best. But it wasn’t easy—far from it. The troops and civilian responders had to move fast and light, while risking injury or death in the hope of reaching trapped climbers before time ran out.

The Japan Self-Defense Forces dispatched 600 troops, 130 vehicles and 17 aircraft to search for mountaineers lost in the ash, rubble and poisonous gases. But after weeks of searching, and with snow on the ground amid thick layers of volcanic debris, the military had no choice but to end the mission.

The Sept. 27 eruption claimed 56 lives—similar to the Mount St. Helens eruption of 1980, which inflicted 57 deaths. Seven individuals remain missing on Mount Ontake, but the search for them is over until spring.

The mission began on the day of the eruption when Nagano Gov. Shuichi Abe requested assistance from the local 13th Infantry Regiment based out of Matsumoto. Within 45 minutes, a Blackhawk helicopter from the 12th Helicopter Regiment was in the air, scouting the conditions around the volcano.

The first troops on the ground were a 40-member “FAST Force.” They left Camp Matsumoto within hours of the eruption.

Japan’s Ministry of Defense unveiled the FAST Force concept a year ago. The full title is quite a mouthful in Japanese, but its catchier official name stands for First Action Support Force.

Previously, Japan’s military would wait for a request from local governments before dispatching troops. Under the FAST Force concept, rapid reaction teams can leave for affected areas within an hour of a disaster prior to receiving a formal request.

This allows them to get to work immediately. The FAST Force was more than two hours away, and every moment mattered to those trapped on the mountain.

By the end of the first day, 180 troops were in position on the mountain as reinforcements gathered at the nearby Camp Matsumoto. The initial response force also received dedicated air support from four helicopters—two Blackhawks, a Cayuse and a Chinook.