The Hårsfjärden, or Horsfjärden (Swedish pronunciation: [ˈhɔ̂ʂːˌfjæːɖɛn]), is a fjard off the Baltic Sea near Stockholm, Sweden. About 20 kilometres (12 mi) long, it has surface area of 61.5 square kilometres (23.7 sq mi). It is the location of three Swedish naval bases: Märsgarn, Muskö, and Berga. It was the location of the Hårsfjärden incident, during October 1–13, 1982, in which Swedish forces appeared to have trapped a foreign submarine, believed to be Soviet, but the submarine escaped.
https://en.wikipedia.org/wiki/H%C3%A5rsfj%C3%A4rden