Anti-Japanese

The people of Singapore resented Japanese rule. Anti-Japanese groups were formed to fight against the Japanese. For example, the Malayan Communist Party formed the Malayan People's Anti-Japanese Army(MPAJA) to fight against the Japanese in the Malayan Jungle. Members of MPAJA would carry out sudden attacks on the Japanese military whenever they had the chance.

Ivan Lyon (center) celebrating with two other
 members of Z Force following the
 success of Operation "Jaywick".

Another group of forces was known as Z Force led by Major Ivan Lyon infiltrated Singapore Harbour and sank or damaged seven Japanese shipscomprising over 39,000 long tons (40,000 metric tons). Lyon led another operation, codenamed Rimau, with the same objective almost a year later and sank three ships. Lyon and 13 of his men were killed after the Japanese discovered them. The other 10 who participated in the operation were charged with espionage in a kangaroo court and subsequently executed.

There was also another force called Force 136, who was led by Lim Bo Seng, code named Gustavus. They established an espionage network in Malaya and Singapore and gather intelligence about Japanese forces for the Allies. However, Operation Gustavus failed and Lim was captured along with his men. Lim died in prison due to ill-treatment.Force 136 was eventually disbanded after the war. 

Sources: http://en.wikipedia.org/wiki/Japanese_occupation_of_Singapore (Date accessed: 17 Feb 13)
CPDD Ministry Of Education. (2007).Singapore From Settlement To Nation Pre 1819 To 1971. Singapore. Marshall Cavendish Education.