On Saturday, 11 May, the Labour Party agreed to join the national government under Churchill's leadership and he was able to form his war cabinet which, at the outset, was restricted to five members including himself as Prime Minister and Minister of Defence. Attlee relinquished his official role as Leader of the Opposition to become Lord Privy Seal (until 19 February 1942 when he was appointed Deputy Prime Minister) and Greenwood was appointed a Minister without Portfolio. The main problem for Churchill as he became Prime Minister was that he was not the leader of the Conservative Party and so he was obliged to include Chamberlain in the war cabinet, as Lord President of the Council, and to retain Halifax as Foreign Secretary. The war cabinet was augmented by the three service ministers who attended most of its meetings and these were Churchill appointees on whose support he could generally rely. Anthony Eden became Secretary of State for War, Labour's A. V. Alexander succeeded Churchill as First Lord of the Admiralty and the leader of the Liberal Party, Sir Archibald Sinclair, became Secretary of State for Air.