Naval War Arctic Circle: Operation Tarnhelm, all new content for Naval War: Arctic Circle is Now Available on Steam Operation Tarnhelm is the first expansion for the unique real-time strategy game Naval War: Arctic Circle. Named after the mythical helmet of Norse mythology that makes its owner invisible, the new scenarios detail daring attacks. Experience NATO’s offensive deep in Russian territory, and Russia’s devastating counter-attack on Northern Europe. Four additional units will provide new tactics and possibilities. This expansion provides unprecedented firepower with stealth aircraft and new warship designs. Who will rule the waves in the 21st century?