'Grasshopper' was an Allied unrealised contingency plan for Major General Lucian K. Truscott’s US VI Corps to break out of its 'Shingle' lodgement at Anzio, on the west coast of Italy, in an eastward direction toward Littoria-Sezze, in the event that Generaloberst Eberhard von Mackensen’s 14th Army of Generalfeldmarschall Albert Kesselring’s Heeresgruppe 'C' fell back more rapidly than expected after the 'Diadem' advance of Lieutenant General Mark W. Clark’s US 5th Army from the line of the Rapido and Garigliano rivers toward Rome (March/April 1944).
On 5 May General the Hon. Sir Harold Alexander, heading the Allied Armies in Italy command, visited the headquarters of the VI Corps, where Truscott outlined for him the four alternative plans which the corps staff, at Clark’s direction, had developed during the two preceding months. These plans were 'Buffalo', 'Crawdad', 'Grasshopper' and 'Turtle'.
'Grasshopper' outlined an attack to the east in the direction of Littoria-Sezze with the object of making contact with the 5th Army’s main force advancing to the north-west from the Cassino area. Only if troops on the southern front appeared to be bogged down and in need of help to achieve a junction with the 'Shingle' lodgement was 'Grasshopper' to be mounted.