One of the more impressive developments in Arctic shipping is the endeavour to make it 'all year round'. The incredibly hard and thick ice of the winter which for centuries had chased the very idea of navigation from the mind of any sensible sailor, and which caused the dangerous and costly winterings, could now be attacked by means of new, powerful icebreakers and ships. The economic advantage of such possibilities is beyond doubt, because seasonal activity means that capital goods will be used only for a short period, which in tum means that capital yields only a part of its potential return, because even if some icebreakers went south a number of them remained unemployed during the winter. Equally, harbour equipment in the Arctic can be used only for a short period, so its capacity has to be larger than in ports that can be used in winter to achieve the same results. Moreover, lengthening the season is a simple way of increasing shipping in the Arctic. Since effective occupation of the Arctic remains difficult, the political weight of this kind of economic activity is still great; exploration and shipping are the pillars of sovereignty in the Arctic, especially where the Soviet Union is concerned.