The 'sortie', his 43rd operational flight, consisted of 367 Lancasters supported by 13 Mosquitos. The marking and bombing, from a relatively low 8,000 feet (2440m), were accurate and severe damage was inflicted on Pforzheim: 1,825 tons (1854 tonnes) of bombs were dropped in 22 minutes. The post-war British Bombing Survey Unit estimated that 83% of the town's built-up area was destroyed, probably the greatest proportion of a city destroyed in any one raid during the war. Ten Lancasters were lost and two more crashed in France.