In April and August 1854 ten British naval ships made several reconnaissance surveys on the waters near Sveaborg (see the map of 1855). From that time there are on the southern tip of Drumsö (Lauttasaari) inscriptions cut on the rock. These are most probably done by local defenders.
On Aug. 6, 1855, the Anglo-French fleet lead by Admirals Richard S. Dundas on Duke of Wellington and Charles Penaud on Tourville arrived at Sveaborg and grouped themselves at an appropriate distance from the fortress. In the morning of August 9 they began shelling at the fortress of Sveaborg, after a morning religious service. The sailors singing a hymn were heard in the city. The fire was extremely severe. The cannons in Sveaborg were so outdated, that they only could return the fire at a close range and were not able to reach the ships. The fire finally ceased on Saturday morning, Aug. 11, 5:00 AM. The cannonade resulted only in small material damages to Sveaborg, but 63 men and non-commisioned officers were killed. In total, 17,000 shells were fired towards Sveaborg, 1,000 towards Drumsö (Lauttasaari), and 3,000 towards the island of Santahamina (Sandhamn). In Lauttasaari, one of the defenders on the island was killed. He was first buried as "An Unknown Soldier" on the island. The firing was not aimed at the city, which thus suffered hardly any damages. The city people even watched the bombardment (picture below) from high places in the city. When the shelling ceased but fleet remained still there, a minor panic broke out in the city. It was assumed that the city is the next target. However, on the 13th of August in the morning, the warships sailed off. Some contemporary news reports in London and Paris newspapers, describing Sveaborg and Helsingfors (Helsinki) being levelled to ashes, were a little bit exaggerated.
An English officer's, George Quinnell's memorial and grave (a photo, by John Lagerstedt) on the island of Isosaari (Stora Mjölö) outside Helsinki. He served on HMS Amphion and was killed during a reconnaissance survey on June 22, 1855. Later, in 1905, a memorial (a recent photo, by Ove Enqvist) to fallen and died 22 British marines was erected on the island of Mäkiluoto (Makilo, also known as MacElliott in memory of a 17th century Scottish captain) situating outside C. Porkkala ab. 40 km to the west of Helsinki. That island was used as a recreation site during the war operations. The British casualties were 33 in total. The French suffered none. A memorial to fallen Russian soldiers was raised in 1855 on the island of Santahamina. It was designed by a Russian sculptor of Baltic-German ancestry, Baron Peter Clodt von Jürgensburg. (He, by the way, was uncle to Elisabeth Järnefelt, née Clodt von Jürgensburg, an esteemed patroness in Helsinki literary circles. She was mother of Aino Järnefelt, composer Jean Sibelius' spouse.)
During the war also the island on Naissaar (Nargö, Nargen) 34 km south of the island of Mäkiluoto, on the Estonian coast, then also part of the Russian Empire, was occupied by the Anglo-French forces. There is also a grave of British marines on the island. There is a photo of its pre-war condition in 1930 and the present one (1995) (links to the the Naissaar page of Valdo Praust).
Literature: Basil Greenhill and Ann Giffard: The British Assault on Finland 1854-1855. A Forgotten Naval War. London 1988.