'Ulster' was an Allied double-bluff deception plan created as an outgrowth of 'Ottrington' to deceive the Germans about the real Allied intentions for the assault on the 'Gotisch-Linie' defences (August 1944).

The object of this undertaking by Colonel Dudley W. Clarke’s 'A' Force was to persuade the Germans that the Allies intended to use their surplus of armour for Lieutenant General Sir Oliver Leese’s British 8^th Army to attack to the north along the east coast of Italy on the Adriatic Sea, so diverting the attention of the Germans from the centre, where the real offensive was to be launched, toward the east coast, so that Lieutenant General Mark W. Clark’s US 5^th Army could make a frontal assault on the 'Gotisch-Linie' defences with a thrust through the Futa pass to Bologna.

'Ottrington' had been run in conjunction with 'Ferdinand' to support the offensive planned by Field Marshal the Hon. Sir Harold Alexander’s Allied Armies in Italy command on the 'Gotisch-Linie' defences. As initially planned, this offensive was to breach the German defences in the centre, in the area of Florence, and pave the way to a drive on Bologna, and the 'story' promulgated by 'Ottrington' was that the Allied offensive would in fact be made on the Adriatic end in the Rimini sector, in conjunction with the amphibious left hook into the Gulf of Genoa that was basic to 'Ferdinand'.

'Ottrington' was fully under way at a time early in August, with extensive fake radio traffic and more than 100 dummy tanks and supporting increasing the apparent strength of the Allies' right wing, when Alexander changed his mind and decided to attack on the right wing after all. This demanded the quick creation and implementation of 'Ulster', which was the first and only major double-bluff undertaking by the 'A' Force: the build-up of 'Ottrington' was gradually revealed as a fake in the hope that the Germans would deduce that the main attack would in fact be made in the centre. Clarke was unhappy with the need for a double-bluff effort which, in the event, did not deceive Generalfeldmarschall Albert Kesselring, the Oberbefehlshaber 'Südwest', for a copy of the message of Lieutenant General Sir Oliver Leese, commander of the British 8^th Army, to his troops fell into the hands of German intelligence and revealed that the offensive on the Adriatic sector was the main drive.