The three flattops - USS Ronald Reagan, USS Nimitz and USS Theodore Roosevelt - entered the operational area, called the Korea Theater of Operations (KTO), for the four-day maneuvers slated to end Tuesday.
The U.S. Navy's previous training operation involving three carriers was in the vicinity of Guam in the Western Pacific in 2007 during the Valiant Shield exercise.
Also to be mobilized are 11 U.S. Aegis ships and seven South Korean warships.
Tensions over North Korea's weapons programme have surged in recent months, as Pyongyang carried out a sixth nuclear test - by far its largest to date - and test fired dozens of missiles, some capable of reaching the USA mainland.
American leaders, including President Donald Trump, have warned the belligerent regime not to "underestimate" or "test" USA strength.
The US has been sending its strategic assets, also including long-range bombers, to the region more frequently for patrols or drills amid accelerating North Korean efforts to expand its nuclear weapons program. And do not try us.The weapons you're acquiring are not making you safer, they are putting your regime in grave danger. The US administration thinks China's economic leverage over North Korea is the key to strong-arming Pyongyang into halting its nuclear weapons and missile programmes. "Every step you take down this dark path increases the peril you face".
Ever since US President Donald Trump and North Korean leader Kim Jong-un's feud broke out in public, barbs have been exchanged nearly regularly between the two nations.
"Reckless remarks by an old lunatic like Trump will never scare us or stop our advance", the North's Foreign Ministry said in a statement.
The harsh words between the leaders have escalated in recent months after North Korea threatened to launch missiles toward the U.S. territory of Guam.