An observant witness of the fight between the Danish and Austrian squadrons off Heligoland on 9th May 1864 was the Royal Navy frigate Aurora. Aurora, commanded by Captain Sir Leopold McClintock, was despatched to Heligoland on receipt of news that an Austrian squadron was on its way to the North Sea.

The Danish cause attracted widespread sympathy in Britain throughout the conflict with Austria and the North German Confederation: indeed, the Prime Minister, Palmerston, and his Foreign Secretary, Russell, strongly favoured some form of armed intervention on Denmark's behalf but could carry neither the Cabinet nor, for that matter, Queen Victoria with them.

More importantly, neither could ignore the advice of Britain's senior military advisor, the Commander-in-Chief of the army, the Duke of Cambridge, that military intervention was impracticable given the reduced state of the army. British impotence on land was not going to deprive Palmerston of a show of belligerence however. He told Austria's ambassador in London that the passage of Austrian warships through the Channel would be "an affront and insult to England" and that any attempt to enter the Baltic would be opposed by a more powerful British fleet.

In the meantime, Aurora was ordered to Heligoland to mount guard over the territory acquired from Denmark in 1814, whilst Admiral Dacres' Channel Fleet was tasked with shadowing the main Austrian fleet when it entered the Downs.

The arrival of Captain Tegetthoff's advance squadron at Cuxhaven on 4th May did not go unmonitored. McClintock left Heligoland in the tender Black Eagle to observe the Austrian ships as they lay at anchor.

He did so out of uniform, hoping to remain inconspicuous, whilst Aurora remained on station. As soon as it became clear that the Austrians were preparing to put to sea again, McClintock returned to the Aurora and, weighing anchor, positioned himself outside Cuxhaven in readiness for their departure.

On 7th May the Austrian ships slowly made their way out of harbour. For a moment Tegetthoff appears to have mistaken Aurora for a Danish vessel as he steered towards her under full sail. He quickly turned away however when he realised his mistake.

On the following day McClintock sighted Suenson's North Sea squadron and, after putting a lieutenant aboard the Danish flagship, Niels Juel, learned of their intention to engage the Austrian's the next day.

Around noon on 9th May the opposing squadrons steamed into view south of Heligoland. McClintock immediately got under way and took up a position three miles offshore so as to clearly establish the limits of British territorial waters. As the fleets closed to within range of each other McClintock ascended Aurora's main topmast to watch the action develop. Crowds of spectators lined the shoreline as well hoping to catch sight of the ensuing battle. Distance and the smoke of gunfire obscured the view however.

At around 3.40 p.m. the Austrian flagship, Schwarzenberg, was seen emerging from the smoke with her foremast, rigging and forecastle ablaze, closely followed by other units of the Austrian squadron and the Danes, who continued firing at Tegetthoff's fleeing ships. Suenson finally broke off the action at around 4.30 when McClintock interposed Aurora between the two antagonists, though the Danish ships remained on station for a time to watch over any sudden Austrian attempt to leave the sanctuary of neutral waters.

It was clear however that both Schwarzenburg and Radetzky were seriously damaged: indeed, Schwarzenburg's foretop collapsed as she sailed past Aurora towards Heligoland. During the night McClintock watched attempts to extinguish the flames and make the ships seaworthy. He offered Tegetthoff medical assistance to tend his wounded but this was rejected. Tegetthoff appears to have suspected McClintock's motives.

A few days earlier, on their way north, the Prussian gunboat Seehund, attached to Tegetthoff's squadron, ran aground and suffered significant damage when under a British pilot entering Ramsgate harbour. Tegetthoff apparently considered this to have been a malicious act on the part of the British and became wary of accepting further offers of help. Later that evening McClintock sent Black Eagle home to England with despatches announcing a Danish victory. A few hours later, blacked out and under cover of darkness, Tegetthoff left British waters to return to Cuxhaven.

Did Aurora's presence prevent Suenson finishing off his enemy? International law concerning the rights of a belligerent to pursue enemy vessels into neutral waters was by no means codified at this time. And there were plenty of precedents for its violation - especially by the Royal Navy. In 1759 Admiral Boscawen pursued a French squadron into the neutral Portuguese waters of Lagos Bay and burnt and captured several enemy ships.

And in 1940 HMS Cossack flouted Norwegian neutrality to rescue British POWs on board the German supply ship Altmark in Jössingfjord. A nation's right to have its waters respected depended in reality on its capacity to enforce its neutrality by force of arms. Many in Britain would have welcomed the destruction of the Austrian squadron, but not at the expense of liberties being taken with British sovereignty. The country was especially sensitive to neutrality issues at the time following a dispute with the USA during their secessionist war when a British ship, Trent, was intercepted by a US vessel on the high seas and Confederate agents forcibly removed.

Palmerston threatened war with the Northern States until Lincoln's government issued a fulsome apology. A strongly worded protest, as well as some sabre-rattling, would undoubtedly have followed any Danish incursions into Heligoland waters, but in view of Palmerston's public stance in favour of Denmark's cause, and Britain's strategic interests, any stronger action seems unlikely. As it was, by her presence, Aurora ensured that no diplomatic complications ensued, with the result that when news of the Danish victory was announced in the House of Commons that same day it met with a degree of acclamation which would not have shamed a British naval triumph.