During the Second World War my father sailed on a Royal Naval warship escorting Arctic Convoys. Merchant ships sailed from UK and USA to the northern Soviet ports of Arkhangelsk and Murmansk to deliver vital supplies under the Lend-Lease programme and were escorted by warships for protection.
The route around occupied Norway was particularly dangerous. There were plentiful German forces in the air and on and under the sea. Severe weather was common - they were frequently sailing in fog through drift ice. There were strong currents to contend with and the mixing of cold and warm waters made the use of sonar equipment awkward. Sailing at night in constant darkness meant that navigation was difficult and convoy cohesion hard to maintain. Daylight brought the ever-present threat of attack from air and sea.
Bitter cold - enough to remove flesh from unprotected hands