In Thailand, Malaya and other countries in the South-East-Asia region, a round of sudden squalls of rain falls every day. Out of a clear sky it suddenly becomes misty, one expects big drops of rain to fall, it becomes a cloudburst. It sweeps everything away in its fall, but after some ten minutes it stops. The clouds clear off and with sunlight filling the neighbourhood the temperature rises, pools on the ground soon dry up before one's very eyes. Such squalls become frequent, intervals between them brief, it seems to go on pouring in a series of rainstorms. Such is the rainy season.

The rainy season in the Thailand-Burma regions usually lasts from May until the end of August, In Japan it lasts a long time so the volume of rain there is large. Particularly in the Three Pagodas Pass region the rainfall in this Tenanasserim belt approaches the world's heaviest rainfall of over 200 ml a day, with occasional rare cloudbursts with 100 ml falling within an hour. In some months a total of 2,000 ml is reached; in Japan this equals a year's average rainfall. In the dry season there were no cloudy skies and the way it cleared up was a marvel. The rainy season was also called the period of monsoons.

When the rainy season opened the surface-drainage of the roads became bad, rainwater accumulated, it got very muddy. Cars had their wheels trapped in quagmires, unable to move. Automobile accidents often piled up and in the end it became extremely difficult to get through at all. Over the deep ruts even bullock-carts with their wide diameter wheels could barely get through. The engineers could move on foot only. Prisoners-of-war and coolies moved blindly on from Kamburi to Wanyai and from Wanyai to Kinsaiyok carrying their heavy baggage, trudging on, soaked by the rain. In single file they stumbled on all mixed together, engineers, prisoners, coolies, Japanese troops aiming at the frontier. These troops carried stripped-down mountain-guns and heavy machine-guns on their shoulders, trudging on in silence carrying equipment-parts on their backs.