'Plan Dog' was the US contingency plan developed by the US Navy for the USA to work with the UK in an offensive strategy against Germany and Italy while remaining on the strategic defensive against Japan (November 1940).

The 'Plan Dog' memorandum was written in 1940 Admiral Harold R. Stark, the Chief of Naval Operations, and considered the strategic situation of the USA becoming embroiled in a two-front war against Germany and Italy in Europe and Japan in the Pacific. The memorandum laid out the USA’s primary options, and suggested that the USA should fight a defensive war in the Pacific against Italy while giving strategic priority to the defeat of Germany and Italy in Europe. As such, the memorandum was a key element in laying the basis for the later USA’s later 'Germany first' grand strategic policy.

The plan had its origins in the USA’s 'Color-coded War Plans' of the 1920s and 1930s when, during this period between the two wold wars, the Joint Planning Committee (later the Joint Chiefs-of-Staff Committee) had devised a series of contingency plans for dealing with the outbreak of war with various countries. The most elaborate of these was 'Orange', which was concerned with the possibility of war with Japan.

Given the nature of world events in the later part of the 1930s, including the start of the 2^nd Sino-Japanese War in 1937, the Molotov-Ribbentrop Pact of 1939, and the German conquest of Poland and western Europe in 1939/40, US planners came to appreciate that there was a very real possibility that the USA might face a two-front war in Europe and the Pacific.

Based on the concept of a one-front war, 'Orange' was therefore withdrawn and five 'Rainbow' plans were promulgated. Unlike the earlier 'Color-coded War Plans', which had all been based on the assumption of only a single opponent, the 'Rainbow' plans contemplated possibility of fighting several opponents, and also the need to defend other western hemisphere nations and to aid the UK.

What came known as the 'Plan Dog Memorandum' was posited on the conditions described in the 'Rainbow-5' war plan, and laid out four possible scenarios, in paragraphs A to D, for US involvement in World War II.

A concerned itself with the defence of the western hemisphere, B on an offensive in the Pacific against Japan while remaining on the defensive in the Atlantic, C on an equal commitment in both the Atlantic and Pacific, and D on an offensive in the Atlantic against Germany and Italy while remaining on the defensive in the Pacific.

The memorandum was submitted to President Franklin D. Roosevelt on 12 November 1940 with the recommendation that the USA should adopt option D (or 'Dog' in the joint US Army and US Navy phonetic alphabet).

Stark added that 'I believe that the continued existence of the British Empire, combined with building up a strong protection in our home areas, will do most to ensure the status quo in the Western Hemisphere, and to promote our principal national interests. As I have previously stated, I also believe that Great Britain requires from us very great help in the Atlantic, and possibly even on the continents of Europe or Africa, if she is to be enabled to survive. In my opinion Alternatives (A), (B), and (C) will most probably not provide the necessary degree of assistance, and, therefore, if we undertake war, that Alternative (D) is likely to be the most fruitful for the United States, particularly if we enter the war at an early date. Initially, the offensive measures adopted would, necessarily, be purely naval. Even should we intervene, final victory in Europe is not certain. I believe that the chances for success are in our favor, particularly if we insist upon full equality in the political and military direction of the war.'

Stark also suggested in the memorandum that until the outbreak of hostilities, the USA should adopt Alternative (A) with the words 'Until such time as the United States should decide to engage its full forces in war, I recommend that we pursue a course that will most rapidly increase the military strength of both the Army and the Navy, that is to say, adopt Alternative (A) without hostilities.'

Alternative (D) gained the support of the US Army and, implicitly rather than explicitly, of Roosevelt, who did not ever formally endorse it. By the end of 1940, therefore, there was consensus at the highest political and military levels in the USA for the placement of the strategic focus on Germany. At a meeting on 17 January 1941, Roosevelt concluded that the primary objective must be to maintain the supply lines to UK and ordered the US Navy to prepare for the escort of convoys. A few weeks after the Japanese 'Ai' attack on Pearl Harbor in December 1941, at the 'Arcadia' first Washington conference between the USA and UK, the USA adopted the recommendations of the memorandum in the form of the 'Germany first' policy. Although the USA did not go entirely on the defensive in the Pacific as the memorandum recommended, throughout the war the demands of the European theatre received a higher priority in the allocation of US resources.