no avail as, in September, Germany mobilised to invade the Sudetenland in Czechoslovakia. Churchill visited Chamberlain at Downing Street and urged him to tell Germany that Britain would declare war if the Germans invaded Czechoslovak territory; Chamberlain was not willing to do this. On 30 September, Chamberlain signed up to the Munich Agreement, agreeing to allow German annexation of the Sudetenland. Speaking in the House of Commons on 5 October, Churchill called the agreement "a total and unmitigated defeat". Following the final dismemberment of Czechoslovakia in March 1939, Churchill and his supporters called for the foundation of a national coalition. His popularity increased and people began to agitate for his return to office. First Lord of the Admiralty: September 1939 to May 1940 The Phoney War and the Norwegian Campaign On 3 September 1939, the day Britain declared war on Germany, Chamberlain reappointed Churchill as First Lord of the Admiralty and he joined Chamberlain's war cabinet. Churchill later claimed that the Board of the Admiralty sent a signal to the Fleet: "Winston is back". As First Lord, Churchill was one of the highest-profile ministers during the so-called "Phoney War", when the only significant action by British forces was at sea. Churchill was ebullient after the Battle of the River Plate on 13 December 1939 and afterwards welcomed home the crews, congratulating them on "a brilliant sea fight" and saying that their actions in a cold, dark winter had "warmed the cockles of the British heart". On 16 February 1940, Churchill personally ordered Captain Philip Vian of the destroyer to board the German supply ship in Norwegian waters freeing 299 captured British merchant seamen who had been captured by the . These actions, supplemented by his speeches, considerably enhanced Churchill's reputation. He was concerned about German naval activity in the Baltic Sea and initially wanted to send a naval force there but this was soon changed to a plan, codenamed Operation Wilfred, to mine Norwegian waters and stop iron ore shipments from Narvik to Germany. There were disagreements about mining, both in the war cabinet and with the French government. As a result, Wilfred was delayed until 8 April 1940, the day before the German invasion of Norway was launched. The Norway Debate and Chamberlain's resignation After the Allies failed to prevent the German occupation of Norway, the Commons held an open debate from 7 to 9 May on the government's