Operation Gustavus was aimed at establishing an espionage network in Malaya and Singapore to gather intelligence about Japanese activities, and thereby aid the British in Operation Zipper – the code name for their plan to take back Singapore from the Japanese.

On 24 May 1943, the first group of Force 136 agents, codenamed Gustavus I and led by John Davis, arrived in Perak on board the Dutch submarine O 24.
The O 24 would rendezvous with Gustavus I again in September and November 1943 to transfer supplies and personnel from Gustavus IV and V respectively.
Its sister ship, the O 23, under Captain Richard Broome, transported Gustavus II and Gustavus III to Malaya on 25 June and 4 August 1943 respectively.
Lim arrived in Malaya on 2 November 1943 as part of Gustavus V. He travelled under the alias "Tan Choon Lim" (陳春林; Chén Chūnlín) to avoid identification and claimed to be a businessman when he passed through checkpoints.

In Perak, Davis and Lim re-established contact with Major Freddie Chapman, who was part of a British unit that stayed behind after the Malayan Campaign and had been carrying out small-scale attacks against the Japanese in Malaya.
They also met guerrilla fighters of the Malayan People's Anti-Japanese Army (MPAJA), including the Malayan communists Chin Peng and Lai Teck.
They reached an agreement that the resistance group would be placed under British command in exchange for weapons, supplies and training.
One of the Chinese provision shops in Ipoh, Jian Yik Jan (建益棧; Jiàn Yì Zhàn), was used as an Allied espionage base.
Communication between the agents was done through smuggling messages in empty toothpaste tubes, salted fish and diaries.

Operation Gustavus failed before the agents managed to achieve any results.
A communist guerrilla who was captured by the Japanese in January 1944 revealed the existence of the Allied spy network operating on Pangkor Island.
In response, the Japanese launched a full-scale counter-espionage operation on the island.
By late March 1944, more than 200 soldiers were on the island.
On 24 March, the Kempeitai arrested a fisherman, Chua Koon Eng (蔡群英; Cài Qúnyīng), at Teluk Murrek on the Perak coast.
Chua was working on Pangkor Island when Li Han-kwong (李權光; Lǐ Hànguāng) of Force 136 approached him and requested to use his boat for their communications.
Chua confessed and implicated Li in the spy ring.
The Japanese laid a trap for Li (who had already escaped Pangkor by then) and, using Chua as bait, captured him shortly after.
Under duress, Li confirmed Chua's story but managed to avoid adding anything the Japanese already knew.
The Kempeitai took Li to Ipoh in the hope that he would reveal more information.
However, Li managed to escape on 26 March 1944 into the jungle.
The Kempeitai went on an all-out search for Li and other Force 136 members, eventually leading to Lim's capture.
The entire spy network was destroyed by 31 March 1944 and was not reestablished until February 1945.
Operation Gustavus was aimed at establishing an espionage network in Malaya and Singapore to gather intelligence about Japanese activities, and thereby aid the British in Operation Zipper – the code name for their plan to take back Singapore from the Japanese.
On 24 May 1943, the first group of Force 136 agents, codenamed Gustavus I and led by John Davis, arrived in Perak on board the Dutch submarine O 24. The O 24 would rendezvous with Gustavus I again in September and November 1943 to transfer supplies and personnel from Gustavus IV and V respectively. Its sister ship, the O 23, under Captain Richard Broome, transported Gustavus II and Gustavus III to Malaya on 25 June and 4 August 1943 respectively. Lim arrived in Malaya on 2 November 1943 as part of Gustavus V. He travelled under the alias "Tan Choon Lim" (陳春林; Chén Chūnlín) to avoid identification and claimed to be a businessman when he passed through checkpoints.
In Perak, Davis and Lim re-established contact with Major Freddie Chapman, who was part of a British unit that stayed behind after the Malayan Campaign and had been carrying out small-scale attacks against the Japanese in Malaya. They also met guerrilla fighters of the Malayan People's Anti-Japanese Army (MPAJA), including the Malayan communists Chin Peng and Lai Teck. They reached an agreement that the resistance group would be placed under British command in exchange for weapons, supplies and training. One of the Chinese provision shops in Ipoh, Jian Yik Jan (建益棧; Jiàn Yì Zhàn), was used as an Allied espionage base. Communication between the agents was done through smuggling messages in empty toothpaste tubes, salted fish and diaries.
Operation Gustavus failed before the agents managed to achieve any results. A communist guerrilla who was captured by the Japanese in January 1944 revealed the existence of the Allied spy network operating on Pangkor Island. In response, the Japanese launched a full-scale counter-espionage operation on the island. By late March 1944, more than 200 soldiers were on the island. On 24 March, the Kempeitai arrested a fisherman, Chua Koon Eng (蔡群英; Cài Qúnyīng), at Teluk Murrek on the Perak coast. Chua was working on Pangkor Island when Li Han-kwong (李權光; Lǐ Hànguāng) of Force 136 approached him and requested to use his boat for their communications. Chua confessed and implicated Li in the spy ring. The Japanese laid a trap for Li (who had already escaped Pangkor by then) and, using Chua as bait, captured him shortly after. Under duress, Li confirmed Chua's story but managed to avoid adding anything the Japanese already knew. The Kempeitai took Li to Ipoh in the hope that he would reveal more information. However, Li managed to escape on 26 March 1944 into the jungle. The Kempeitai went on an all-out search for Li and other Force 136 members, eventually leading to Lim's capture. The entire spy network was destroyed by 31 March 1944 and was not reestablished until February 1945.
Lim Bo Seng