The howl of the sirens gave way to a piercing scream: the Trumpets of Jericho, horns fixed to the undercarriage of a Stuka dive-bomber which gave the aircraft its trademark sound as it plummeted towards its target; many men found the ear-splitting noise far more terrifying than the bombs the German aircraft hurled with remarkable accuracy.

The attack on Portland Harbour was the opening blow in what Germans called the Kanalkampf – the Battle of the Channel.

The head of the Luftwaffe, Hermann Göring, committed two air corps – in the region of 550 bombers, dive-bombers and fighters – to sweep all shipping from the Channel, one precursor to any German invasion.

For this first strike, just 20 Junkers 87s escorted by twin-engined Messerschmitt 110 fighters were sent across the Channel.

Their attack on Portland lasted eight minutes. In that time Foylebank was struck by an estimated 20 bombs.

One of the first to hit wounded 23-year-old Leading Seaman Jack Mantle, a Londoner educated in Southampton. Mantle had already demonstrated his bravery – and keen eye – by downing a German aircraft while protecting a convoy in the Thames Estuary.

A career sailor with six years’ service under his belt, Mantle joined the newly-commissioned Foylebank directly from the RN’s gunnery school in Portsmouth, HMS Excellent.

He was put in charge of the starboard ‘pom pom’, spewing out 20mm shells at his attackers at the rate of more than 100 rounds a minute. He continued to fire despite a shattered leg and the electrical system failing, forcing the guns to be operated by hand.

Mantle sustained further wounds as he inspired his shipmates to fight back before collapsing as the Stukas departed. Half of the barrels on his gun were out of action.

Both Jack Mantle and HMS Foylebank succumbed to their wounds. The gunner died shortly after the attack, the vessel the following day, taking more than 70 men with her.

80th anniversary of the only Naval Battle of Britain VC winner

Topic: PeopleRemembrance

Thursday July 4 1940. Six days before the Battle of Britain officially began. The crew of HMS Foylebank were settling into the day’s routine in Portland Harbour – as their breakfast settled in their stomachs.

It was a little after 8.30am when the howl of air-raid sirens sounded across Portland and the crew of HMS Foylebank, a 5,500-tonne merchantman turned into a floating anti-aircraft battery to defend the harbour and naval base, went to their action stations.

One month had passed since the Dunkirk evacuation, a fortnight since France had sued for peace. More than half a million British and Allied troops had been brought back from France, but almost all their equipment had been left behind.

The euphoria of Dunkirk spirit had passed, replaced by a stark realisation that Britain was locked in a mortal struggle for her very existence.

Churchill had vowed Britons would “defend our island, whatever the cost may be” fighting “on the beaches… on the landing grounds… in the fields and in the streets, we shall fight in the hills; we shall never surrender.” Withstanding the Nazi onslaught would be the nation’s “finest hour”, but the premier warned his people that the “whole fury and might of the enemy” would be hurled at them.

And now, this Thursday morning, it began.

Mantle’s superior thought his actions worthy of the Conspicuous Gallantry Medal. That was elevated to the Victoria Cross, announced in September 1940 and presented to his parents by George VI the following summer.

“Jack didn’t seem to be the heroic type,” his surprised mother Jeannie May said. “He was a quiet, earnest boy. He had an intense dislike of pain, and was always afraid of the dentist . . .”

Jack Mantle remains the only sailor to win the Victoria Cross for actions in the UK itself. The medal can be seen at the National Museum of the Royal Navy in Portsmouth, while the seaman lays at rest in Royal Naval Cemetery on Portland.

This is the first of three features on the role of the Royal Navy in the Battle of Britain.