However, on 2 July 1940, when Germany began to suspect that England had no intention of surrendering, Hitler's chief military aide, Field Marshal Wilhem Keitel, issued instructions to all three services to prepare for an invasion of Britain. The invasion was to be code-named "Operation Sea Lion". Two weeks later Hitler issued directive No. 16 for the Conduct of the War. Directive No. 16 began:.
"As England, in spite of the hopelessness of her military position, has so far not shown herself willing to come to any compromise, I have decided to begin to prepare for, and if necessary to carry out, an invasion of England. This operation is dictated by the necessity of elimination Great Britain as a base from which the war against Germany can be fought , and if necessary the island will be occupied.".
The operation against Britain had been divided into three main phases. The first phase was the campaign over the English Channel to sink all British merchant shipping, Royal Navy ships, bases and installations, and to destroy or drive out of the sky any RAF fighters that sought to prevent these maneuvers. Second would be a massive onslaught to paralyze Britain's air powers once and for all by obliterating all RAF fields, defenses and aircraft factories in a gigantic combined bomber and fighter blitz. This operation was code named "Eagle Attack". In the third and final phase, the Luftwaffe would cover and help implement Operation Sea Lion. The Germans were oblivious to the fact that the English had two secrets that would come to aid them greatly in the coming months. The first of these was a new invention called the radar.
The British radar system consisted of two primary types of radar. The first was used for detecting high flying aircraft at long range. Nicknamed "Chain Home", this system was useful for spotting German aerial formations as they assembled over the French coast. However, this network was incapable of spotting planes that came in low over the channel.