The Malay campaign consisted of many heroic battles by retreating Commonwealth forces in a very difficult terrain with heavy tolls and atrocities by advancing Japanese forces including the Parit Sulong Massacre and the Alexandra Hospital Massacre. The fall of Singapore was a disaster, surrendering to a smaller force. I can only imagine the disappointment felt by those who fought only to lay down their arms and endure years of suffering. Also resulting in the subsequent murder of many thousands of Chinese during the Sook Ching Operation
Wiki has a good account and is a good read, jump off into sub headings for more information.
https://en.wikipedia.org/wiki/Malayan_campaign
https://en.wikipedia.org/wiki/Battle_of_Singapore