'Modicum' was the US mission to the UK to present the 'Marshall memorandum' on the eventual Allied invasion of Europe to Prime Minister Winston Churchill, Deputy Prime Minister Clement Attlee, Foreign Secretary Anthony Eden and General Sir Alan Brooke, Chief of the Imperial General Staff (8 April 1942).

Prepared by General George C. Marshall, the US Army chief-of-staff, the memorandum had three main elements: firstly, it advised the immediate implementation of 'Bolero' to move 30 US divisions (including six armoured divisions) and appropriate air power to the UK within 12 months; secondly, it urged the launch on 1 April 1943 of 'Round-up' to land 30 US and 18 British divisions (including three armoured divisions) in France between Boulogne and Le Havre with a first wave of six divisions and paratroops, reinforced at the rate of 100,000 men per week to secure the primary objective of a major lodgement in France from Calais to Deauville via Arras, St Quentin, Soissons and Paris; and thirdly, it called for the start of 'Sledgehammer' on 15 September 1943 to take Cherbourg and the Cotentin peninsula.

The British reaction was decidedly mixed, and the only portion of the Marshall memorandum to receive full approval was 'Bolero'.