These reports were of fundamental importance in the war against the U-boats and give a complete picture of antisubmarine operations, planning and the ongoing situation as far as the Royal Navy was concerned during the war. Each report was published for the attention of all ships and was essential to all as a guide to events, and to counter-measures and tactics. Each report gives details of what the U-boats were doing throughout the month and the losses caused to merchant shipping as well as warships. The report then details the countermeasures taken against the U-boats by surface ships and aircraft. The U-boats ranged from their French bases over the North Atlantic and also passed into the Mediterranean and the Pacific and Indian oceans. The main battle however was fought on the convoy routes between Britain and the United States. The convoys themselves are covered in some detail and it is not difficult to find out the composition of virtually all convoys that sailed in the war, together with attacks and losses. The reports also contain narratives which cover specific incidents relating to U-boats, the surface ships fighting them and the aircraft operating against them. These are often first-person accounts, or taken from signals sent to the Admiralty by the participant ships or aircraft. Luckily for the modern naval historian the reports also include significant information on equipment and tactics. Innovations brought in by both sides are described as are other very interesting aspects of this decisive battle. There can be no doubt that the Battle of the Atlantic was one of the most important conflicts to be fought. Had the German U-boats been able to close the convoy routes between the United States and Great Britain, Britain would have starved and the invasion of France in 1944 might never have taken place. In all these are some of the most exciting and significant reports that MLRS has ever reprinted. This is not to belittle other very detailed reports and analyses which MLRS reprints; however, the crucial nature of the war at sea in the Atlantic against the U-boats has to be recognised as a victory that was hard-won but absolutely essential to the defeat of Germany.   Volume I covers the period from September 1939 to June 1940.