About a minute later, the Enola Gay was hit by the first shockwave. The plane’s aluminum skin made a sharp, cracking retort, as if someone had swung a very large sledgehammer at the fuselage from outside. The aircraft jerked and trembled, but held together. Tibbets estimated that the hit was equivalent in force to about two-and-one-half Gs. This first shockwave was followed quickly by a second, moderately less violent—it was an echo of the first, having struck the ground and rebounded upward.
