One of the few resources not in short supply was oil, supplies originally intended for Europe were filling British storage facilities. Considerable effort and enthusiasm was put into making use of petroleum products as a weapon of war. The British Army had not had any flame throwers since the end of the First World War, but a significant number were hastily improvised from pressure greasing equipment acquired from garages. Although limited in range they were considered to be reasonably effective. There were many ideas for using petroleum on a larger scale and although many of the ideas proved fruitless a number of practical petroleum warfare weapons were developed. Mobile land barrages comprised surplus bulk storage tanks mounted on trucks, the contents of which could be drained into a sunken road and ignited. A Static Flame Trap was prepared with perforated pipes running down the side of a road connected to a 600-gallon tank at an elevated position. Usually, gravity sufficed but in a few cases a pump assisted in spraying the mixture of oil and petrol. A flame fougasse was a 40-gallon drum dug into the roadside and camouflaged. It would be placed at a location such as a corner, steep incline or roadblock where vehicles would be obliged to slow down. Guncotton provided the propellant charge which, when triggered, caused the weapon to shoot a flame 10 feet (3 m) wide and 30 yards (30 m) long. They were usually deployed in batteries of four barrels. The Demigasse was similar to the Flame Fougasse, but was placed in the open. 50,000 flame fougasse barrels were installed at 7,000 sites mostly in southern England and at a further 2,000 sites in Scotland.Banks, 1946, p38. The Hedge Hopper was a barrel of petroleum mixture with an explosive charge placed underneath slightly off centre. On firing, the barrel would be projected ten feet (3 m) into the air and over a hedge or wall behind which it had been hidden.. Early experiments with floating petroleum on the sea and igniting it were not entirely successful: the fuel was difficult to ignite, large quantifies of it were required to cover even modest areas of sea and the weapon was easily disrupted by waves. However, the potential was clear; by early 1941 a flame barrage technique was developed. Rather than attempting to ignite oil floating on water, nozzles were placed above high water mark with pumps producing sufficient pressure to spray fuel which produced a roaring wall of flame over, rather than on, the water. Such installations consumed considerable resources and although this weapon was impressive, its network of pipes was very vulnerable to any pre-landing bombardment; General Brooke did not consider it to be effective. Initially ambitions plans were cut back to cover just a few miles of beaches..
In the event of an invasion, the Navy would have sailed to the landing places — possibly taking several days to get there. It is now known that the Germans planned to land on the southern coast of England, one reason for choosing this site was that the narrow seas of the English Channel could be blocked off with mines, u-boats and torpedo boats. While German naval forces and the Luftwaffe could doubtless have extracted a high price from the Royal Navy they could not have hoped to prevent interference with attempts to land a second wave of troops and supplies that would have been essential to German success — even if, by then, the Germans had captured a port essential for bringing in significant heavy equipment. In this scenario, British land forces would have faced the Germans on somewhat more equal terms than might otherwise have been the case and it was only necessary to delay the German advance, preventing a collapse until the German land forces were, at least temporarily, isolated by the Royal Navy and then mounting a counter attack.
Scholarly consideration of the likely outcome of a German invasion, including wargames held at Sandhurst in 1974 generally agree that while German forces would have been able to land and gain a significant bridgehead, the intervention of the British navy would be decisive and, even with the most optimistic assumptions, the German army would not have penetrated further than GHQ line and would ultimately have been defeated.
