During the Second World War a major part of the strategy of the Grand Alliance was shipping. The Germans fully appreciated the vulnerability of this and their attack on it, largely by means of submarines, became known as the Battle of the Atlantic. The attack was overcome, with some difficulty, by a number of means. One, which remained generally unknown until the 1970s, was the decryption of German coded signals, now usually called Ultra. Subsequent histories often tended to attribute the outcome of the Battle largely to the operation of this factor almost by itself, sometimes because of a lack of rigorous analysis and also because of a failure to set this important subject into the full and complex contexts in which it operated. This study rectifies this deficiency, setting out the full story of the series of campaigns and carefully assessing the complicated pattern of factors, thus allowing a much more balanced understanding of code-breaking.

This is the Naval Staff History of "Operation Dynamo," originally published internally in 1949. British ships evacuated nearly 100,000 men of the BEF from the beaches, and over 200,000 from harbours. Other nations' vessels carried more than 30,000. Scores of ships were lost during the operation, and many more were seriously damaged, but a very large proportion of the British Army had been rescued in the teeth of continual air attack, from an every-shrinking perimeter. The troops then had to be transported across the Channel in the face of enemy aircraft, mines, torpedoes, and fire from the shore, through waters unlit and strewn with wrecks.
Although the campaign was, in Churchill's words, "an unmitigated defeat," there is much to take pride in, and many lessons to be learned from this operation. The appedices include a list of ships which took part in "Operation Dynamo," and numbers of troops transported.