The unit was constructed at the Crichton-Vulcan shipyard in Turku, Finland, and named after the mythological hero Ilmarinen from the Finnish national epic, the Kalevala.

During the early inter-war period the Finnish Navy consisted of some 30 ex-Russian vessels, most of them taken as war-trophies following the civil war.

Prior to World War II, the fleet renewal program led to the acquisition or construction of five submarines, four torpedo boats, and two coastal defense ships.

They were designed by the Dutch company NV Ingenieurskantoor voor Scheepsbouw (a front for German interests circumventing the Treaty of Versailles), and were optimized for operations in the archipelagos of the Baltic Sea.

Coastal defence ships were particularly popular in the Nordic countries, and began serving in the navies of Denmark, Sweden and Norway early in the 20th century.

Their sizes were around 4,000 tons, main armament consisted of guns between 210 and 240 mm (8 and 9 in), the armor corresponded to that of armoured cruisers, and speeds were between 15 and 18 knots (28 and 33 km/h; 17 and 21 mph).

Maximum speed was 14.5 knots (26.9 km/h; 16.7 mph), and range was limited by the vessels' carrying capacity of only 93 tonnes of diesel oil.

The four 254 mm (10 in) Bofors guns were massive for vessels of this size, and they could hurl a 225 kg (496 lb) shell up to 31 kilometres (19 mi).

The purpose of the coastal defence ships was to prevent landing operations and naval blockades that threatened vital sea trade.

Thanks to the construction of vast defensive systems during the czarist era, Finland had strong coastal artillery in permanent positions.

When the Winter War erupted, Ilmarinen and her sister ship Väinämöinen were dispatched to Åland in order to guard against a possible invasion.

They were painted white to prevent Soviet bomber crews from spotting them, but were targeted by aircraft on several occasions, resulting in one death and several injuries.

The two Finnish coastal defence ship participated in Operation Nordwind on 13 September 1941, in which German forces were to take the Estonian islands of Saaremaa and Hiiumaa.

A group of Finnish and German ships were to be used in a diversionary operation to lure the Soviet fleet into battle – away from the real invasion force coming up from the south.