2015 will be a year of grim centenaries. They should be handled with care.

For connoisseurs of historic wartime atrocities, 2015 will be a bumper year. It marks the centenary of strategic aerial bombing, the first serious use of lethal gas as a weapon of war and the start of the Ottoman Empire’s genocide of Armenians.

But to judge by the legal press of 1915, it was two other atrocities that aroused British public opinion – the sinking of the Cunard liner Lusitania and the execution of nurse Edith Cavell. Both were committed by the Germans. Both caused outrage. And yet, a century on, it seems the perpetrators had the law on their side. 

The sinking of the Lusitania by a German U-boat off southern Ireland on 7 May 1915 with the loss of more than 1,200 lives remains one of the most controversial episodes of the first world war. Conspiracy theorists hold that the ship was sacrificed at the secret order of Winston Churchill, first lord of the admiralty, in order that outrage about the deaths of American passengers would bring the US into the war.

Churchill almost certainly entertained such ideas, but the evidence suggests the Lusitania was lost more through naval incompetence than conspiracy. Moreover, the ship was a legitimate military target. 

European navies had gone to war observing the quaintly named ‘cruiser rules’ governing the taking of prizes on the high seas. While noted by the 1907 Hague Convention, they essentially related to the era of Horatio Hornblower, in which merchant ships were supposed to heave-to in response to a shot across their bows and allow their cargoes to be inspected for contraband.

Submarines rendered those rules obsolete, and in case there was no doubt Churchill had ordered merchant ships to fight back, by ramming if necessary. 

In any case, the Lusitania was rated as an auxiliary cruiser, built to admiralty specifications and equipped with mountings for six-inch guns (though, apparently, not the guns themselves). On its final voyage, it was carrying large quantities of rifle ammunition, which was on its cargo manifest, as well as artillery shells and explosives, which were not. A number of Canadian troops were also on board. 

Despite these holes in its case, the British authorities were quick to exploit the sinking. The coroner in Kinsale, Ireland, where the bodies were washed up - then of course part of the United Kingdom - recorded a verdict indicting Kaiser Wilhelm II of Germany on a charge of ‘wilful and wholesale murder’.

But that was only the beginning of proceedings, which included a semi-public inquiry presided over by Lord Mersey, the High Court judge who had presided over the Titanic inquiry in 1912, and a protracted lawsuit in the US. These involved the admiralty lying about the explosive cargo, which was understandable in wartime, and attempting to shift blame for the disaster onto the Lusitania’s captain, William Turner, which was not. 

Evidence for the American proceedings was taken in June 1917 at the Law Society’s Hall in Chancery Lane. Liverpool firm Hill, Dickinson & Co (still very much in business) acted for Cunard, and did its best on behalf of captain Turner, a master mariner of the old school who had worked his way up from the foc’sle of square-riggers and had little time for politicians or lawyers.

But by then the US was in the war and it was Churchill’s version of the tragedy that entered the history books, largely because he wrote them. 

The case of Edith Cavell is an even more straightforward one of faux outrage. The 49-year-old British nurse had helped some 200 British and allied soldiers escape from German-occupied Belgium. She was arrested by the occupation authorities in August 1915 and charged with treason under the German military code. 

A Brussels lawyer, Sadi Kirschen, undertook Cavell’s defence - at some risk to himself - but Cavell defiantly admitted the charges, was sentenced to death, and shot on 12 October. Despite worldwide condemnation, the sentence was justifiable under contemporary law. 

By acting as a belligerent Cavell had forfeited the protection of the first Geneva Convention; it could be argued that she had imperilled the activities of all personnel serving under the Red Cross. The British authorities would have done the same; indeed they were to behave with similar lack of concern for public relations after the Easter rising in Dublin the following year. 

Tellingly, after the war no one was tried for Cavell’s killing, or indeed the sinking of the Lusitania. Kaiser Wilhelm lived out his retirement in the Netherlands, where he died in 1941 with a Wehrmacht sentry at his gate.

But Cavell’s body was brought back for burial in Norwich Cathedral and she is commemorated in innumerable nursing institutions.

There is also a famous statue just off Trafalgar Square, which, a few years ago I saw decorated with the flags of an unpleasant Middle Eastern regime. The women responsible told me they were pacifists and claimed Cavell for their cause – indeed they seemed under the impression she had been executed by the British for pacifism, more or less the direct opposite of the truth.

But a wartime atrocity will generally find someone to claim it for their cause. That’s as true now as it was in 1915.

Michael Cross is Gazette news editor