Its aim was to find out what might have happened had Nazi Germany launched Operation Sea Lion, their planned invasion of southeast England during World War II, in September 1940.
The British umpires were Air Chief Marshal Christopher Foxley-Norris, Rear Admiral Teddy Gueritz and Major General Glyn Gilbert.
The people who played the British Home Forces Commander-in-Chief, General Sir Alan Brooke, and the First Lord of the Admiralty, Dudley Pound, are not recorded.
By this device, the game designers were able to justify the counterfactual of Sea Lion being launched, even though actual air superiority had not been achieved.
[3] These were: Andy Callan, John Davis, Michael Orr, Dennis Barr, Nigel de Lee and Tony Thomas.
"[7] However, in 1940 the British might well have had this level of knowledge due to their top-secret Ultra code breaking efforts against the Germans, which had not yet been made public at the time of the 1974 wargame.
In any event, the 1974 British wargame team took full advantage of their intelligence coup and the two day delay by moving four more divisions to Saffron Walden, Newbury, Crowborough and Royal Tunbridge Wells to bolster the nine already in East Anglia, Kent and Sussex.
They were spotted by a British armed trawler at 11 p.m., The Cromwell warning was issued half an hour later (and the church bells rung), and at midnight the Home Fleet was ordered south.
The German first echelon attack was launched at dawn on 22 September 1940 and consisted of 8,000 airborne troops and 80,000 infantry landing in amphibious operations.
The German invasion fleet only suffered minor losses due to motor torpedo boats, however, about 25% of the barges used for the first echelon were lost after being destroyed on the beaches.
The larger ships of the Royal Navy's Home Fleet (including battleships, heavy cruisers and aircraft carriers) were not yet committed due to their vulnerability to air attack and U-boats.
British and Commonwealth forces were moved to fully engage in the battle with the first counterattack on 23 September, halting the advance of the Germans towards Hastings and recapturing the western bank of Newhaven.
By dusk on 23 September, the Germans had 10 divisions ashore, but most were halted by counterattacks, and were awaiting the remainder of their equipment, stores and personnel (critically including tanks and heavy artillery) on the second and third echelons.
The decision to dispatch the second and third echelon shipping of the German invasion was held back in hopes that a possible capture of either Dover or Newhaven could be achieved.