This was an Allied deception plan designed to conceal the weakening of the Allied forces in Italy, as formations and landing craft were redeployed from this theatre to the UK for 'Overlord', by the notional transfer of other formations to the Mediterranean theatre (January 1944).
This was possibly the most important deception created by Colonel John H. Bevan’s London Controlling Section (the northern European counterpart of Brigadier Dudley W. Clarke’s Mediterranean-based 'A' Force) to pave the way toward 'Overlord' and the great deceptions associated with that invasion.
'Foynes' was a plan to conceal from the Germans the weakening of the Allied position in the Mediterranean by the transfer of eight veteran formations (the US 1st, 9th, 2nd Armored and 82nd Airborne Divisions, and the British 50th, 51st, 7th Armoured and 1st Airborne Divisions) from that theatre to the UK to serve as the experienced core of the forces being gathered for 'Overlord'. 'Foynes' therefore sought to preserve a fiction of undiminished Allied strength in the Mediterranean by the despatch to that theatre of three genuine divisions (the Canadian 5th Armoured Division, and the US 85th and 88th Divisions) and adding to the Allied order of battle in the theatre four notional divisions (the British 40th, 42nd and 57th Divisions and the 5th Airborne Division). The 'story' also included indications that another two notional divisions (British 61st [later 68th] Division and US 46th Division) were being retained at a high level of readiness for later despatch but were never used.
The notional movements of these formations to the Mediterranean were carefully planned to coincide with the passage of real convoys, and appropriate administrative measures were taken as though real movements were involved.
Associated with these notional troop movements was a plan which failed somewhat comically. The Germans maintained 12 observation posts, some on each side of the Strait of Gibraltar, and these were brightly lit at night to show the silhouettes of all passing ships. To suggest to them that the highly visible westward movement of landing craft was being offset by an eastward movement of replacements from the USA, the US actor turned deception specialist Douglas Fairbanks and one Harry Gummer, the latter newly posted to Gibraltar to form an 'A' Force outstation at 'the Rock', came up with the concept of laying a smokescreen onto which false silhouettes would be projected by means of a sort of magic lantern device. This proved unfeasible.
Eventually the London Controlling Section drew up 'Gotham', under which a number of dummy inflatable landing craft would be visibly carried on the decks of merchant ships passing eastward through the Strait of Gibraltar. This was trialled on a convoy which departed Liverpool early in January, but when the ship encountered heavy weather the dummies bounced around like large balloons, and this signalled the end of 'Gotham'.
Bevan also proposed a double bluff for concealing the movement of the veteran divisions to England, by giving publicity to the homecoming of well-known British units and using double-agent channels to tell the Germans that this was in fact deceptive cover for a build-up of the Allied forces in the Mediterranean theatre for an invasion of the Balkans. The British Chiefs-of-Staff rejected the concept, however, and all that could be done was to keep the real movements as secret as possible. In April 1944, thinking that the Germans must surely know by now that the eight divisions were in England, Bevan allowed the Germans to learn this via well-established double agents and authorised a public announcement of their presence in the UK. The Germans had in fact not suspected the movement.
This reflected the tenacity, or perhaps obstinacy, of Oberst Alexis Freiherr von Roenne at Fremde Heere 'West', who was executed in October 1944 for his part in the 20 July plot to assassinate Adolf Hitler. Before this, once a unit had been entered into his order of battle it remained there until it was proven to be elsewhere. The intelligence staff of Generalfeldmarschall Albert Kesselring’s Heeresgruppe 'C' in Italy in fact reported the disappareance of formations extracted from Italy, but von Roenne refused to change their disposition in his order of battle. von Roenne’s report of 31 December 1943, which was intercepted and decrypted to become vital 'Ultra' intelligence for the Allies, advised that there was no indication at all that major forces were being transported away from the Mediterranean area, and in February von Roenne asked the Abwehr intelligence service to locate the supposedly missing divisions.
So far as landing craft were concerned, von Roenne conceded total defeat in admitting, late in October 1943, that as there was in effect no German aerial reconnaissance in the Mediterranean theatre, he had no information on their present locations. And even six months later, with the Allied armies, navies and air forces gathering in England, von Roenne reported that he could not estimate the number of landing craft available in British ports on the grounds that the Allies possessed a masterly capability for the camouflaging of their landing craft over a wide area, and that the Germans should therefore expect these craft still to be in the Western Mediterranean.