At the start of the Second World War, the standard British flight gear was outdated, having been intended mostly for use in open-cockpit aircraft. As early aircraft types were replaced by the Perspex-canopied Hurricanes and Spitfires, pilot equipment technology failed to keep pace. During the Battle of Britain, there was a lack of standardisation in the flight gear used by pilots. Both government issue items and private purchase equipment were used by pilots, dependent on supply and preference. Perhaps no items lacked uniformity as much as flying goggles. Wartime photographs document great variation in the types used during combat. Some pilots wore the basic goggles that dated back to the Great War, while others endured the Mark III version that featured a large leather face pad intended for open-cockpit flying. The goggles most often associated with the air battles of 1940 are the government-supplied Mark IIIa goggles first introduced in 1935. The Mark IIIa goggles (below) had a metal frame with leather nose support and a velveteen cushion pad; but they were often criticised by pilots because of the propensity for the celluloid lens inserts to become scratched during combat operations. The curvature of the lenses also distorted vision. Because the goggles had been designed independently of the standard flying helmet of the day, they did not fit well. RAF pilots lobbied for improvement and the Air Ministry responded with an improved design that better served the needs of the pilots, introducing the famous split-lens Mark IV goggles in June 1940. Improved variations of these split-lens goggles continued to appear up to the end of the war, culminating in the iconic Mark VIII split-lens goggles (above).