From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
While the opponent is in the air, Goku charges a one-handed Kamehameha and fires it at the ground to launch himself up into the air. Then, he shouts, "I'm going to put everything I got into this move!" and clenches his hand into an energy-powered fist. A silhouette of a Great Ape (which is said to represent Goku's hidden powers) appears as Goku puts his fist forward and punches through the opponent, inflicting a huge amount of damage.
Goku used this attack to defeat Piccolo Daimao. After breaking Goku's legs and left arm, Piccolo Daimao flew high up into the air and charged back down to kill the crippled Goku. However, with his right arm still intact, Goku launched himself up at Piccolo Daimao with a Kamehameha and attacked him with the Penetrate! punch. Although Piccolo Daimao braced for impact, the force of Goku's attack was too powerful and the evil Namekian was left with a large, gaping hole in his chest. However, Piccolo Daimao spat out the egg of his final offspring and encouraged his son to avenge his death by killing Goku before succumbing to his injuries and blowing up.
Prior to his battle with Piccolo Daimao, Goku used a similar technique to destroy the Red Ribbon robot which the recently self-promoted Black piloted, resulting in Black’s death. This attack was the same as Penetrate! but with two hands extended forward rather than one (probably since Goku had no usage of his other limbs at this point when fighting Piccolo Daimao).
Son Gohan also used a technique nearly identical to Goku's attack on Black to rip a hole in Garlic Jr.'s body followed by blasting him with a Masenko. Since Garlic Jr. was immortal, however, the attack barely phased him.
Goku used another similar technique to destroy God Guardon in Dragon Ball Z Gaiden: Saiya-jin Zetsumetsu Keikaku.
The techniques Dragon Fist and Super Dragon Fist are believed to have been derived from the Penetrate! technique.
In Dragon Ball GT, Goku used the Dragon Fist to defeat Super No. 17 in a similar fashion to the way he killed Piccolo Daimao decades earlier (by ripping a hole through the chest). Although the Penetrate! punch was strong enough to cause Piccolo Daimao to explode, Super No. 17 was able to survive the Dragon Fist and it required a Kamehameha from Goku to finally finish the Super No. 17.