Commander James Lennox-King joined the Royal New Zealand Volunteer Reserve in March 1931 as an Ordinary Seaman. In 1940 having attained the rank of Lieutenant he was posted to the training establishments HMS VICTORY and HMS DRAKE in Britain for training. He then posted to the destroyer HMS ANTHONY, where Lennox-King was a Gunnery Officer and consequently Mentioned In Despatches in regard to operations against the Vichy French during the take over of Madagascar.
During the D-Day landings on the Normandy coast Lennox-King was once again a Gunnery Officer, this time onboard the destroyer HMS VIRAGO. This ship was consequently sent out to what was then known as the Far East; upon the cessation of World War II Lennox-King returned to New Zealand where he rejoined the Auckland Division of the RNZVR.
In November 1952 Lennox-King was commissioned into the Royal New Zealand Navy, spending time on fishery protection vessels and as Staff Officer at the shore establishment HMNZS PEGASUS. In addition he was involved with “Operation Deep Freeze” and became Captain of the wooden hulled Antarctic supply ship HMNZS ENDEAVOUR commissioned into the RNZN in August 1956. Later he travelled to the United States as part of the commissioning party of the new Antarctic tanker HMNZS ENDEAVOUR, the converted USS NAMAKAGON when she commissioned into the RNZN October 1962. Subsequently he made several trips to Antarctica onboard this vessel.
James Lennox-King retired from the RNZN in April 1966 having attained the rank of Commander.