The three Navy carriers — accompanied by more than 20,000 sailors, hundreds of aircraft and an array of destroyers and cruisers — will all be underway in the Japan-based 7th Fleet's area of operations.

It's an unusual occurrence and comes at a time of rising tension with North Korea, which has repeatedly threatened the United States and continued provocative missile tests during the past several months.

The last time the Navy operated three carrier groups together was 2007, Marine Lt. Gen. Kenneth McKenzie Jr. told reporters Thursday. The West Coast-based carriers Nimitz and Theodore Roosevelt will be joined by the Japan-based carrier Ronald Reagan.

A joint exercise involving the three carriers has not been publicly announced, but Navy officials who spoke on the condition of anonymity said the planning is underway.