No aspect of the Second World War has become more controversial in recent years than Britain''s Strategic Air Offensive against Germany. Argument has raged over both the morality of mass bombing of heavily populated cities; over its effectiveness in seriously impairing Germany''s war effort and over the horrendous casualty rates caused - both to civilians on the ground, and to the aircrew of RAF Bomber Command who lost some 52,000 men - a higher attrition rate than any other branch of the armed services. In assessing the campaign the official British history of the offensive, of which this is the fourth and final volume, is indispensible. This book contains the background documents - some highly secret - on which the previous narratives of the campaign are based. There are chapters on radar - that war-winning British invention - on navigational aids; on bombs and bombsights and on post-war British and US surveys into the effectiveness of their devastating attacks. There are minutes, mem oranda, operational orders and reports from the key figures involved in directing the air war: Sir Arthur ''B omber'' Harris himself; Sir John Dill, Sir Charles Portal and from the father of the RAF, Lord Trenchard. There are also important papers from the ''other side of the hill '' - the Germans, including police reports on the firestorm which swept away the port of Hamburg; and personal reports from Armaments MInister Albert Speer to Hitler on the results of the RAF blitz on German oil and fuel production in June 1944. The book also contains fascinating facts and figures on losses to aircrew, tonnage of bombs dropped, the RAF"s order of battle and estimates of damage done and civilian casualties. Altogether this essential book gives the hard facts on which any conclusions about Britain''s air offensive must ultimately be based.