'Magneto' was the Allied cover designation for the 'big three' conference at Yalta in Crimea (4/11 February 1945).

'Cricket' (ii) and 'Magneto' were together known as 'Argonaut', in which the three leaders who met were Prime Minister Winston Churchill of the UK, President Franklin D. Roosevelt of the USA and Premier Iosif Stalin of the USSR.

The British delegation was installed in Prince Vorontsov’s castle of Alupka, while the US delegation was housed in the former tsars' palace with Roosevelt staying at the Livadia Palace, which was the location for the meetings. Key subordinate members of the delegations were the Americans Edward Stettinius and Averell Harriman, the British Anthony Eden and Alexander Cadogan, and the Soviet Vyacheslav Molotov.

A number of key decisions was taken at the conference. There was agreement that the priority must be the unconditional surrender of Germany which, after the end of hostilities, would be divided into four occupied zones; Berlin, the German capital, would be similarly divided between the four occupying powers. Stalin agreed to let France get the fourth occupation zone in Germany and Austria, carved out from the British and US zones, and France would also be granted a seat in the Allied Control Council. Germany would undergo demilitarisation and denazification. An inter-Allied reparations council would be established in Moscow.

The post-war status of Poland was discussed, but the situation was complicated by the fact that by this time Poland was under the control of the Soviet army. It was agreed to reorganise the Provisional Polish Government set up by the Soviet army through the inclusion of other groups to create the Polish Provisional Government of National Unity, and to follow this with national elections, even though this process effectively excluded the Polish government-in-exile which had been formed in London. The Polish eastern border should basically follow the Curzon Line, and Poland should receive substantial territorial compensation in the west from Germany.

Citizens of the USSR and Yugoslavia were to be handed over to their respective countries, regardless of their consent.

Roosevelt obtained a commitment by Stalin to participate in the United Nations Organisation once it was agreed that each of the five permanent members of the Security Council would have veto power.

Stalin agreed to enter the war against Japan within 90 days of Germany’s defeat, and the USSR would receive the southern part of Sakhalin island and the Kurile islands group after the defeat of Japan.

The 'Magneto' conference was the last great inter-Allied conference before the end of the war, and the last foreign visit by Roosevelt who, to observers, appeared ill and exhausted. Arguably, Roosevelt’s most important achievement was to ensure Soviet participation in the United Nations Organisation, which he achieved at the price of granting veto power to each permanent member of the Security Council, a condition that significantly weakened the UN.

Another of his objectives was to bring the USSR into the war against Japan, as the effectiveness of the atomic bomb had yet to be proved.

The Soviet army had already seized most of eastern Europe, so Stalin essentially got everything he wanted, especially in Poland: a government which could be manipulated, territorial concessions, and a significant sphere of influence as a 'buffer zone'. In this process, the freedom of small nations was somehow expendable and sacrificed 'for the sake of stability', which would mean that the Baltic states of Latvia, Lithuania and Estonia would remain under Soviet occupation.