'Jael' was an Allied deception concept created to convince the Germans that the focus of forthcoming Allied amphibious landing operations would continue to be in the Mediterranean area rather than North-West Europe (August/November 1943).

'Jael' was developed in light of the decisions reached at the 'Quadrant' conference held in Quebec during August 1943. The most important of these decisions was that 'Overlord' in the spring of 1944 would remain the main Allied effort for that year, and the plan also reflected several planning conclusions reached during the late summer period of 1943.

One of the more significant of these conclusions was the likelihood that the Germans would become increasingly concerned about the possibility that the remaining neutral countries of Europe, notably Portugal, Spain, Sweden and Turkey, but not Switzerland, might enter the war on the Allied side. Another was that the London Controlling Section (a secret department established in September 1941 within the Joint Planning Staff at the offices of the War Cabinet to co-ordinate Allied strategic military deception) should address in detail only the first or strategic phase and therefore leave COSSAC (Chief-of-Staff to the Supreme Allied Commander) with responsibility for the specifics of the second or operational phase.

After dismissing the idea of exaggerating Allied strength, 'Jael' stated its object as being to cause the Germans to dispose their forces in a manner which would keep German strength in France below the level over which COSSAC currently believed that 'Overlord' would not be feasible.

The concept on which 'Jael' was to be based was to be that while Allied forces in the UK were large, they included only a few divisions with an amphibious capability and also several divisions being trained for mountain rather than amphibious warfare; that a number of experienced divisions were to be transferred from the Mediterranean, where they would be replaced by new divisions; that landing craft transferred from the Mediterranean would be used primarily for training; that while US forces would be arriving in the UK during the winter of 1943/44 in great numbers, a considerable proportion of them would be bomber crews and ground personnel for 'Pointblank', as well as administrative and garrison troops; and that the British were so short of manpower that they were cannibalising their divisions to keep the most important of them up to strength.

The 'Jael' plan was therefore to suggest that caution was the key element of Allied strategy, and that within this the Allies placed great faith in the efficacy of the 'Pointblank' bombing offensive, and therefore hoped that the combination of 'Pointblank', a Soviet summer offensive and their own operations in the Mediterranean would weaken the German strength in France to the point that an Allied invasion would be feasible. The plan would thus persuade the Germans that the Allies would in all probability not attempt a cross-Channel invasion before the summer of 1944, but in the shorter term intended to invade southern Norway and Denmark as they knew these to be more weakly held than France; and that Allied forces in the Mediterranean were greater than was in fact the case, and would be used to secure northern Italy and establish bomber bases there, to invade the Balkans through Istria and across the Adriatic, to mount a simultaneous amphibious attack in the eastern half of the Mediterranean with the aid of US forces coming directly from the USA, and to invade the Balkans through Turkey. It was also hoped to persuade the Germans that southern France would be invaded only if the Allies were satisfied that they would encounter little opposition.

The Allies assumed that about one month before the launch of 'Overlord' the Germans would come to appreciate that a cross-Channel assault would shortly be launched, and at this point 'Jael' should suggest that the invasion would be directed primarily on the Pas de Calais and Belgium; that Allied forces were still concentrated for an attack on Norway and Denmark in an undertaking in which they still hoped to involve Sweden; that the Balkan, eastern Mediterranean and Turkish operations were imminent; and that the Allies had approached Spain for permission to land in the Biscay ports and Barcelona and then to move troops across Spain to invade south-western France.

'Jael' was submitted to the Joint Planning Staff on 22 September by the LCS’s controlling officer, Colonel John Bevan, who suggested that representatives of COSSAC and AFHQ (Allied Forces HQ) also be involved with consideration of the plan. COSSAC’s main concern with 'Jael' was the sense making diplomatic approaches to the neutrals. The plan was also considered in Washington, where other concerns were raised, and on 26 October the British agreed to defer consideration of 'Jael' until after the 'Eureka' and 'Sextant' conferences in Tehran and Cairo in about a month’s time. By that time the 'Jael' concept was deemed obsolete and the plan was replaced by 'Bodyguard'.