Five main British Antarctic Survey stations were occupied throughout the year. These were Faraday and Halley (the two geophysical observatories), Signy (the main biological station), Grytviken (a multi-disciplinary sub-Antarctic station) and Rothera (the centre for air operations). The 1977 winter passed uneventfully and the stations were relieved in the 1977–78 summer, as usual, by the two Survey ships RRS John Biscoe and RRS Bransfield and two Twin Otter aircraft. However, ice conditions in the Antarctic Peninsula area were severe; although Halley was relieved without too much difficulty at the beginning of January, the ships were unable to reach Rothera until the end of February. By that time it was too late for major building operations, and the third and final phase of the development of Rothera (the construction of another large building) had to be postponed.