1 Discard any hammer with mushroomed or chipped face or with cracks in the claw or eye sections. 2  Wear safety glasses or goggles, or a face shield (with safety glasses or goggles).  Strike a hammer blow squarely with the striking face parallel to the surface being struck.
The first jet airplane was the Heinkel He 178 made in Germany in 1939, right before the outbreak of World War II .
In Russia, Igor Sikorsky built the first air giant, a four-engine plane that was the forerunner of the multiengine strategic bombers of World War I. The French military began experimenting with aerial bombing in 1912, as did the British in 1913.