'Chesterfield' (i) was an Allied deception operation designed to aid the offensive of Lieutenant General Mark W. Clark’s 5^th Army to the south of the 'Gustav-Linie' defences by suggesting that an amphibious assault was to be made behind the Germans' right flank at Gaeta just to the north of the Garigliano river’s mouth on the Tyrrhenian Sea (December 1943).

The short-term objective of Clark’s 5^th Army was to drive the last parts of Generaloberst Heinrich-Gottfried von Vietinghoff-Scheel’s German 10^th Army back into the 'Gustav-Linie' defences, and to aid this a radio deception, visible preparations and a report from the 'Gilbert' double agent that the Allies were preparing a British brigade in the Bay of Naples to undertake this outflanking movement.