Blenheim squadrons were still in immediate and high demand after their withdrawal from France as part of the British action during the Norwegian Campaign. Typically operating from bases in the northern areas of the British mainland, such as RAF Lossiemouth, flying for extended periods over the North Sea led to the weather posing almost as much of a risk as enemy combatants, particularly as most of the Blenheim IVs lacked any heating or de-icing systems; in response, some aircraft were later equipped with boilers fixed onto the starboard engine exhaust. A sizeable number of losses occurred, caused by both enemy action and mid-air engine failures due to icing.