To be really ignored by history you ought to make sure there's a lifesize bronze statue of you set in a London square. The city is littered with plaques, horses and helmeted figures, most of whom go unnoticed until they are decorated with a traffic cone or a green Mohican turf. There's one, the National Memorial of the Merchant Navy and Fishing Fleets near the Tower of London, which is a restrained and reflective place to visit.

The memorial, in a sunken garden by the Thames, records the names of 32,000 seafarers of the Merchant Navy and fishing fleets who died in both world wars and have no grave but the sea. In the second world war the Merchant Navy had a higher ratio of casualties that any of the armed services. The total sacrifice during the 20th century is known to be more than 46,000 men and women.

One of the statues guarding the dead is, I've just learned, modelled on Bosun Kenneth Stewart, a man from the Isle of Lewis. He served on first world war minesweepers, was shipwrecked while serving on a passenger liner in the second world war and went on to save the lives of three others overcome by carbon monoxide fumes in the hold of a cargo ship in 1943. For his contribution to the Merchant Navy he was awarded a British Empire Medal and became a renowned peacetime bosun with the New Zealand Shipping Company It's fitting a Hebridean was chosen to represent the ratings as the island of Lewis lost 20 times as many of its sons at sea as any other part of Britain during the second world war, simply because so many island fishermen were on the Royal Navy Reserve list. The week before war began, 800 Lewis Royal Naval Reservists were mobilised to form the core of professional crews. As a result many islanders were in the front line at the outbreak of hostilities.

Growing up in a village on Lewis among adults who survived the war we were aware of a tangible sense of loss. I remember being surprised as a youngster to discover Rawalpindi was a city in the subcontinent because for years the name was synonymous with maritime tragedy. The sinking of the HMS Rawalpindi, in the first month of the war, knelled the arrival of the first wartime telegram to our village, informing our neighbours and relatives Donald and Lily MacKenzie that their son had been lost.

On October 23, 1939, in mountainous seas in the Iceland-Faroes gap, the Rawalpindi engaged the most powerful naval ship in the world, the German battle-cruiser Scharnhorst. Outgunned, the Rawalpindi, skippered by the father of broadcaster Ludovic Kennedy, Captain Edward Kennedy, refused to heave to and fired her guns with the ship ablaze from stem to stern. Kennedy died in the action along with 237 of his men. Twelve of the gunners on the Rawalpindi were naval reservists from Lewis and eight of them were killed. The four survivors became prisoners of war.

Among the island dead was Murdo MacKenzie, who grew up on the croft next to ours in Swordale. My aunts, who were schoolchildren at the time, still paint a vivid picture of the day the local postmaster took the news to the thatched house next door.

Donald John MacLeod, a maritime historian who documents these island losses, recollects how the shockwaves from that buff-coloured envelope spread. "I was a boy in Uig at the time and I remember the anxiety all over the island," he said. "At first it was thought the 12 Lewis lads had been killed. Then there was information that all the survivors on the German ship, Deutschland, were Scots - this lifted morale but no more was heard and gloom descended again."

And that was an enduring gloom. Within the month the postmaster was back at Donald MacKenzie's blackhouse door in Swordale. A second telegram: his second son, John, another naval reservist, had also been lost at sea.

Such was the extent of island casualties that the London periodical Illustrated sent that quintessential journalist HV Morton to Lewis in the spring of 1940 to profile the "islands of sorrow". The resulting article, carefully clipped and with rusting staples, became a treasured possession in many homes. One picture shows Donald and Lily MacKenzie, my grand-aunt and stepmother to these boys, sharing the load of a peat-laden basket, looking out to the sea that robbed them of two beloved sons.

I've re-read the piece many times and one line from Morton's island dispatch sticks out. "Whole villages have been drained of their youth long before their call-up was due and older men in the reserve have gone too," he wrote. It's staggering to think that young men kept volunteering, presumably with their parents' blessing, despite the kind of news from Valhalla that the sinking of the Rawalpindi and many other merchant ships brought.

When I first started attending the cenotaph services I thought it would be just military types, old buffers and sentimental fools like me. I'm always awed by the crowd of all ages, packed into a hushed Parliament Square and up through Whitehall. Thousands come to remember the war dead and there's a particular poignancy for those whose relatives are in harm's way in Iraq and Afghanistan. This year I'll stop off at Tower Hill, to remember the merchantmen and say hello to the Lewis Bosun.