World War One: The sinking of the SS Belgian Prince 100 years on

Image copyright Hassan family

"We still don't know what happened to Uncle Harry. But we would love to know."

Even down the phone, clear Geordie tones ring out from Mick Laffey - a world away from the accent his County Down-born great-great uncle Capt Henry 'Harry' Hassan would have employed.

Some relatives of the Bangor-born captain, including Mr Laffey, have stayed close to the area of Tyneside where he lived before he disappeared 100 years ago, following the sinking of SS Belgian Prince on 31 July 1917.

It was an event that even in the midst of World War One jumped from the pages of the UK's daily papers.

"A crime unparalleled for fiendish cruelty," "A cold-blooded murder" caused by "submarine savagery" that resulted in the deaths of 38 men in the harsh waves of Atlantic Ocean, almost 200 miles from the west coast of Ireland.

An "outrage" recorded in the minutes of a meeting held by Prime Minster David Lloyd George's war cabinet in the days after.

The details were gruesome - a cargo ship torpedoed by a U-boat, its fleeing crew taken from lifeboats before they could escape.

Their lifejackets confiscated, the crew were assembled on the hull of the submarine before it submerged, leaving all but four of the men to drown.

Three survivors and one more unaccounted for - Capt Henry Hassan, who was taken below the deck of the U-boat before it submerged.

His family never saw or heard from him again.

His name features on Tower Hill Memorial in London, dedicated to mercantile seaman who died in both world wars with no known grave, as well as on Bangor's war memorial.

But his exact fate remains unknown over a century later - did he die in Germany as an unrecorded prisoner of war? Or was he killed when the U-boat carrying him was destroyed by British forces?

Or was he the victim of a ruthless U-boat commander, a "prototype Nazi", who later served on the staff of Heinrich Himmler?

Mr Laffey was "six or seven" when he first heard about "Uncle Harry".

"I was sitting with my nana and asked her if anybody in our family was in the war," he told BBC News NI.

"And she talked about Uncle Harry.

"When she explained what happened, you could tell that it had affected her and the family.

"Her mam would've known Harry, the whole family was touched by what happened, it was a personal tragedy."

His uncle, Philip Burchill, was told the story by his grandfather in 1961 when he asked for help writing a seafaring story for homework.

"I was 11, my grandfather didn't tell me the details of the sinking," he said.

"I remember listening with horror, a few years later, as he told me that the submarine had dived with the crew of the Belgian Prince on its deck."

The story itself only came to be told because of the three fortunate survivors.

Newspaper reports from the time carried the testimony of Chief Engineer Thomas Bowman.

He described the moment the submarine became submerged in the ocean.

"Suddenly, I heard a rush of water and, shouting 'look out, she's sinking,' I jumped into the water," he said.

"Many men went down with the submarine, others swam about.

"Near me was an apprentice, aged 16, shouting for help, I held him up in darkness until about midnight when he became unconscious and died from exposure."

He, along with two others, was taken to the Sailors' Rest in Londonderry, where they were tended to by the maritime charity now known as the Sailors' Society.

The charity marked the 100th anniversary of the sinking of the Belgian Prince with a wreath-laying ceremony last Monday.

"This horrific event is one of the many examples of merchant seafarers paying the ultimate sacrifice to keep supply chains open during times of conflict," said its chief executive Stuart Rivers.

The sinking of the Belgian Prince would have been considered an outrage at the time, said Bangor historian Ian Wilson, although it would also have been an opportunity for the UK government.

"They would have made the most of it for propaganda purposes," he said.

"And it should be remembered that there were things the British did that were just as bad.

"But, certainly, the story of the Belgian Prince is a fascinating though very, very sad story and what happened to Henry Hassan is very, very unusual."

In June 1919, Capt Hassan was declared legally dead.

There are no shortage of theories on what happened to him, although not even Mr Laffey and Mr Burchill agree over which is correct.

He may have been taken to Germany as a prisoner of war, but there is no record of him entering the country or being held there.

The British Red Cross were not notified of his capture.

The most arresting theory surrounds Wilhelm Werner, the commander of U-Boat U55.

Evidence points towards Werner being behind a number of attacks with striking similarities to that of the SS Belgian Prince.

The SS Torrington is believed to have been sunk by U55, with its crew then left helpless on the submarine's hull after the captain was taken below.

Werner was accused of war crimes and fled to Brazil after the war when the Allies demanded his extradition.

He returned to Germany in 1924 before climbing the ranks of the Nazi Party and eventually becoming a part of Heinrich Himmler's personal staff.

It is the U55 that Mr Laffey believes attacked and sunk the Belgian Prince. He believes Werner possibly had Capt Hassan killed.

"He wouldn't have thought twice about getting rid of him (Capt Hassan)," Mr Laffey said.

"He wouldn't want him to be a witness to war crimes, to be able to tell the tale."

Mr Burchill, however, reckoned it was a different U-boat, U44 , that torpedoed the Belgian Prince - and U44 was sunk on 12 August 1917, just 12 days after Capt Hassan disappeared.

He believes "Uncle Harry" was lost when the U44 was destroyed.

This is the theory that a British judge laid out in court in 1918 when he was given leave to presume the death of Capt Hassan.

"If it was friendly fire that caused Uncle Harry's death, then I could accept that, because the alternative must be that it was the U55," said Mr Laffey.

Odds are the fate of Capt Hassan will never be known - but that won't deter his family from keeping the story and his memory alive through any means they can.

In 2014, a local church in Hebburn, near Newcastle, asked for names to be included on a plaque dedicated to those from the area who fought and died in World War One.

"I put his name forward and waited for the day it was unveiled and when I went to see it I scanned down the 30 or so names - and his wasn't on it," said Mr Laffey.

"But then I looked up, and he was at the top on his own. He was the only officer - a master of a ship."