He was "the white-haired hero of Tobruk", a Royal Navy captain from Warminster whose courage in saving men and blazing ships under constant enemy fire made him a legend among the besieged port's brave defenders in World War II.

For months, he fought to help stop the vital North African foothold falling into German and Italian hands until he was fatally injured aboard the last serviceable Allied ship to leave, while ensuring oil storage tanks on shore were destroyed.

Now the medals won by Captain Frank Montem Smith, including a CBE and DSO, are to go under the hammer on October 28, at an auction at Lawrence's of Crewkerne, Somerset. They are expected to sell for between £10,000 and £12,000.

Captain Smith was a former merchant seaman who had served with the Royal Navy in World War I on ships including the early submarine, E39. He returned to the merchant service between the wars, while remaining in the Royal Navy Reserve. When World War II broke out, he was given command of a ship chasing U boats and entered Tobruk shortly before it came under siege in April 1941.

By then, at 47, he was a veteran figure to many of the young officers on the Royal Navy ships providing vital gunfire support, supplies and fresh troops to the beleaguered Allied command.

Maintaining control of Tobruk was vital and it withheld the siege, led by Field Marshall Rommel, for months, before finally falling in 1942.

Among his many extraordinary acts of courage, Captain Smith boarded British merchant vessel Cerion which had been bombed by seven German Stuka planes. Smith led the firefighters who saved the vessel.

Earlier, while still a commander, he boarded a blazing ship carrying aviation fuel to close a vital hatch. Less than three weeks later he boarded SS Tynefield, which was on fire after being bombed, despite behind in the midst of an air raid. He organised officers and crew into dealing with the situation and arranged for it to be towed stern first into wind, containing the fire.

Jeffrey Day, Lawrence's militaria expert, said: "During the final withdrawal from the port on June 12, 1942, he showed great courage and resource in rapidly organising arrangements for the embarkation of Naval ratings and firing of demolition charges, all under heavy fire in periods of immense stress.

"Soon after embarking on the last craft to attempt to leave, he was fatally wounded and died in the harbour he loved so well. German tanks were on shore firing point blank at the vessel which drifted ashore. His CBE and DSO were collected posthumously from Buckingham Palace by his daughter, Wren Joan Smith."

In his autobiography, Admiral Andrew Cunningham wrote: "The tale of our losses on the Tobruk run was mounting steadily but whenever the place is mentioned my mind goes back at once to the naval officer in charge, Captain Frank Montem Smith, CBE, DSO, RD, RNR, outstanding amongst gallant men."

When Captain Smith was hospitalised in Alexandria, Cunningham had offered him the command of a ship but "in his quiet voice he firmly said: 'no sir I would like to go back to Tobruk'."

Warminster-born Captain Smith left a wife, Emily, who lived in Boscombe, Bournemouth. The couple had two children, Edward, who died in 1985, and Joan, who died in the US last year.