The discovery of the electromagnetic waves at the beginning of the century knows applications only in the Thirties in the merchant navy. But once that the soldiers are convinced of the tactical interest of radiodetection, research will be given increasingly important appropriations.
The radars knew since 1941 a crowd of applications. We already evoked the systems for the detection of the air and maritime formations but also to direct the shootings of artillery.
• Thus devices radars were developed by the Anglo-Saxons in order to guide the escadrilles bombers through Europe starting from England. What made it possible to the allied pilots to bombard as much as possible the good objective.
• Radars of air monitoring were installed on large planes. Similar systems also existed for the detection of ships, then for the terrestrial monitoring when technology radar allowed. Many a U-Boot (German submarines) occupied reloading their electric batteries on the surface were thus located and then cast thanks to the airborne radars.
• The Germans tried to counter this new threat by developing the Naxos system which makes it possible the submarines to know if it «is illuminated» by an enemy radar and thus to plunge to escape from the submarine chasers (generally of the destroyers equipped with sonars and anti-submarine grenades).
• The hunters of night were equipped, as well at the Germans as at the Allies, of airborne radar to locate the enemy planes. In the same way the allied bombers were sometimes equipped with small radars in the tail of the apparatus to announce if a hunter had taken it in hunting.
• Finally a cousin of the radar, the sonar uses the same principles of radiodetection but in water. The sonar will be fatal with the supremacy of the submarine in North Atlantic and in the Pacific.

The radar is a rather significant example of many technological «progress» which we believe had with the second world war. In fact, the war allowed to a certain extent to apply scientific discoveries of the beginning of the century. One cannot speak about technological innovation but rather about improvement.