On 19 June 1940, during World War II, Lamb enlisted in the
Second Australian Imperial Force, and was posted to the
2/2nd Pioneer Battalion. The battalion sailed for the Middle East in April 1941, where they engaged the forces of
Vichy France in
Syria. In early 1942, Lamb's battalion and several other units were returning to Australia on board the SS
Orcades, but once the ship landed at
Batavia, they were ordered to defend
Java against Japanese forces which had begun to move through the
Dutch East Indies. The Japanese landed on Java on 28 February, and were
engaged at Leuwiliang by a combined American–British–Australian formation called "Black Force". On 8 March, the Dutch surrendered, and Black Force was ordered to surrender the next day. Lamb was captured as a
prisoner of war and was sent to work on the
Burma Railway in
Thailand. Lamb was still listed as missing in action at time of the
Victorian state election on 12 June 1943, however he was re-elected unopposed to the seat of Lowan. On 14 September, Lamb's twin sister received a letter from him stating that he was in "excellent health" and was being treated well by the Japanese. On 7 December 1943, Lamb died at the Japanese work camp 131 Kilo in Thailand, suffering from malaria, dysentery and malnutrition. Official notification of his death was not received in Australia until nearly nine months later on 1 September 1944. Lamb is buried at the
Thanbyuzayat War Cemetery in Burma (Myanmar). A memorial hall in Horsham was named the Hamilton Lamb Memorial Hall in his honour. Confirmation of Lamb's death triggered
a by-election in the seat of Lowan, with the writ issued on 28 September 1944, and polling on 4 November.
Wilfred Mibus retained the seat for the Country Party. ==Personal life and family==