HE WAS only 20 when he became a national hero - even though his history-making exploits were known to only a small number of people.

Lt-Cmdr David Balme was serving aboard the frigate HMS Bulldog when he led a daring mission that changed the course of the Second World War and saved thousands of lives.

He and some of his fellow crewmen boarded a newly-abandoned German submarine and made a discovery that was dubbed "untold gold".

New Forest Post:

Tucked away in the bowels of the vessel was one of the Enigma code machines that were used to receive top secret signals from Nazi commanders.

The discovery enabled codebreakers at Bletchley Park to intercept and decode all the messages from Germany to its U-boats in the Atlantic.

As a result, Allied convoys taking vital supplies to England were diverted to safer parts of the ocean, preventing huge loss of life.

Lt-Cmdr Balme died four years ago aged 95.

Now a plaque posthumously honouring his achievements has been unveiled at St John's Church, Boldre, to mark the centenary of his birth.

The plaque says: “In loving memory of David Edward Balme. Lieutenant-Commander DSC, RN 1st October 1920 – 3rd January 2016. Boarded German submarine 9 May 1941 recovered cipher material and Enigma machine.”

Lt-Cmdr Balme lived in the parish of Boldre for about 40 years with his wife Susan, who died in September last year aged 93.

New Forest Post:

He earned his place in history after the U-110 was attacked and damaged by HMS Bulldog after surfacing in mid-Atlantic.

The Nazi sailors abandoned their stricken vessel but Lt-Cmdr Balme was warned that "one or two" crewmen could still be aboard.

As the first member of the boarding party to enter the partially-submerged submarine he risked being shot, blown up by a booby trap or drowned.

Relieved to discover the whole crew had fled, Lt-Cmdr Balme began to search the vessel.

He and his fellow sailors returned to Bulldog with a treasure trove of vital intelligence, including an Enigma machine and months' worth of associated cipher material.

In the 1990s Hollywood made a $90m movie, U-571, which was loosely based on his exploits.