Monkey D. Garp is a vice admiral in the Navy, specifically commanding the 153rd Navy branch. Garp possesses numerous combat skills and is highly respected by everyone in the Navy. He is often considered a mentor to many renowned characters in the Navy, including Admiral Kuzan, who is known to be the 10th commander of the Blackbeard Pirates.
It is not an exaggeration to say that Garp is on par with the Admirals in terms of combat prowess. To illustrate this point, let’s examine several key arguments below.

First, let’s compare Garp with Red-Haired Shanks, one of the Four Emperors reigning over the New World. Even though age and health have weakened him compared to his prime, he still stands as a formidable opponent against any other Admiral. During the Marineford War, Shanks proved himself to be a monstrous force that the Navy and the Shichibukai had to unite against in order to fight.
It should be noted that Shanks has yet to fully utilize his Conqueror’s Haki, only employing other types of Haki. This indicates that Shanks remains one of the few Emperors with the potential to turn the tide in battle.
Meanwhile, Garp is also aging like Shanks, but he has not shown any signs of weakness yet. Despite his age, which certainly affects his physical abilities, he is still capable of competing with the Admirals. In fact, this legendary Marine has previously been a direct rival of the Pirate King, Gol D. Roger, who is undoubtedly stronger than the current Admirals.
So, even though Garp’s abilities may have diminished somewhat due to his age, he still possesses the potential to challenge the Admirals and even has the capability to land powerful blows. Garp wields Haki that few characters in the One Piece world can match.

Next, let’s compare Garp with the Dark King Rayleigh. Rayleigh has publicly admitted that he is weaker than Shanks, stating that if the two were to fight, he would likely lose. However, Garp has taken on the role of a mentor to Coby, despite knowing that Rayleigh could easily overpower him. This suggests that Garp has a great deal of confidence in his own strength.