In August 1914 just one week after the outbreak of war, Harold Ozanne was posted to HMS Cressy a 15 year old cruiser which had recently been taken out of reserve. Her crew had been thrown together at short notice and was comprised of older reservists and young Boy Sailors, some only 14 years old, including a whole class of cadets from Dartmouth Naval College

Cressy and her sister ships Aboukir and Hogue were sent to patrol the North Sea off the Netherlands coast. Many senior naval officers pointed out the danger of leaving slow and obsolete warships exposed to the threat of German submarines, and some nick-named the patrol the 'Live Bait Squadron'. But others dismissed the threat, regarding submarines as toys and unproven in battle.

But these three cruisers were soon to be involved in one of the worst naval disasters of the War.

On 22 September they were attacked by a German U-boat. The Aboukir was torpedoed first and sank within 35 minutes. Hogue and Cressy returned to pick up survivors. Whilst stopped in water Hogue was hit by two torpedoes and also began to sink. Cressy then realised the danger and started to move away from the scene, but she was hit and sank within 30 minutes.

Dutch fishing boats rescued 837 men from the sea, including Harold Ozanne, but 1397 men and boys were lost.

Overnight this event changed the world's perception of submarines, put a cloud over the future of the battleship and greatly damaged the reputation of the Royal Navy which until this point had been regarded as almost invincible.

On the morning of 22 September, Cressy and her sisters, Aboukir and Hogue, were on patrol without any escorting destroyers as these had been forced to seek shelter from bad weather. The three sisters were steaming in line abreast about 2,000 yards (1,800 m) apart at a speed of 10 knots (19 km/h; 12 mph). They were not expecting submarine attack, but had lookouts posted and one gun manned on each side to attack any submarines sighted. The weather had moderated earlier that morning and Tyrwhitt was en route to reinforce the cruisers with eight destroyers.

U-9, commanded by Kapitänleutnant Otto Weddigen, had been ordered to attack British transports at Ostend, but had been forced to dive and take shelter from the storm. On surfacing, she spotted the British ships and moved to attack. She fired one torpedo at 06:20 at Aboukir which struck her on the starboard side; the ship's captain thought he had struck a mine and ordered the other two ships to close to transfer his wounded men. Aboukir quickly began listing and capsized around 06:55 despite counterflooding compartments on the opposite side to right her.

As Hogue approached her sinking sister, her captain, Wilmot Nicholson, realized that it had been a submarine attack and signaled Cressy to look for a periscope although his ship continued to close on Aboukir as her crew threw overboard anything that would float to aid the survivors in the water. Having stopped and lowered all her boats, Hogue was struck by two torpedoes around 06:55. The sudden weight loss of the two torpedoes caused U-9 to broach the surface and Hogue's gunners opened fire without effect before the submarine could submerge again. The cruiser capsized about ten minutes after being torpedoed and sank at 07:15.

Cressy attempted to ram the submarine, but did not succeed and resumed her rescue efforts until she too was torpedoed at 07:20. Weddigen had fired two torpedoes from his stern tubes, but only one hit. U-9 had to manoeuvre to bring her bow around with her last torpedo and fired it at a range of about 550 yards (500 m) at 07:30. The torpedo struck on the port side and ruptured several boilers, scalding the men in the compartment. As her sisters had done Cressy took on a heavy list and then capsized before sinking at 07:55. Several Dutch ships began rescuing survivors at 08:30 and were joined by British fishing trawlers before Tyrwhitt and his ships arrived at 10:45.

From all three ships 837 men were rescued and 62 officers and 1,397 enlisted men lost: 560 of those lost were from Cressy.

In 1954 the British government sold the salvage rights to all three ships to a German company and they were subsequently sold again to a Dutch company which began salvaging the wrecks' metal in 2011.