In December 1942 Japan needed a supply route to connect newly acquired territories that stretched from Singapore to the Burma-India border. The almost impenetrable terrain of the River Kwai basin was chosen as the route for a 415 kilometer long Thailand-Burma Railway. Japan brought about 60,000 Allied POWs to work on their railway, along with as many as 200,000 conscripted Asian laborers. In June 1942 work began from both ends. Conditions were brutal, and by the time the line was completed 15 months later, an estimated 16,000 POWs and 100,000 Asian laborers had died working on it. It is said that one worker died for every railroad tie (aka sleeper).
The bridge crossing the Kwai Yai was made famous by the 1957 (fictionalized) movie, "Bridge Over the River Kwai." The steel bridge was built from sections brought from Java and reassembled by POWs. A temporary wooden bridge was built alongside the steel bridge and carried the first train in February 1943. The steel bridge was completed in May 1943. Both bridges were heavily damaged by Allied bombers in 1944 and 1945; the steel bridge was repaired after the war and continues to be in service. It is crossed several times daily by tourist trains; between the trains it is possible to cross the bridge on foot.
As near as I can tell, October 25, 1943, was when the entire railway was opened.
This was a group of Thai school girls. I would like to have gotten them coming towards me with the bridge in the background, but I was positioned wrong for that shot.