Adnan led a 42-strong platoon from the Malay Regiment in the defense of Singapore against the invading Japanese. The soldiers fought at the Battle of Pasir Panjang, at Pasir Panjang Ridge in the Bukit Chandu (Opium Hill) area on 12 February-14, 1942. Although heavily outnumbered, Adnan refused to surrender and urged his men to fight until the end. They held off the Japanese for two days amid heavy enemy shelling and shortages of food and ammunition. Adnan was shot but carried on fighting. After the battle was lost, the wounded Adnan was taken prisoner by Japanese soldiers, who tied him to a cherry tree and bayoneted him to death.
Because of his actions Adnan is currently considered by Malaysians and Singaporeans today as a hero. In their textbooks, he is also credited as the soldier who caught the disguised Indian troops' marching error in four abreast instead of a line of three.
When Singapore surrendered, the Japanese Kempeitai attempted but failed to find and murder Adnan's family in revenge.
Kent Ridge Park, close to the site of the battle, now bears a plaque in commemoration of Lt Adnan Bin Saidi. A museum at Bukit Chandu stands in memory of the bravery of Malay Regiment soldiers. This regiment would later become the Royal Malay Regiment of the Royal Malaysian Army.
His biography was later made into a movie titled: Leftenan Adnan.
Source : Leftenant Adnan Bin Saidi wikipedia.