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The US and South Korea are expected to announce as soon as today that a critical joint military exercise has been scaled back because coronavirus is severely limiting the ability of both nation’s militaries to participate, according to three US officials.

What this could mean: This would be the first major impact of coronavirus on US military readiness according to the officials. Without the full exercise, the US could lose ground in being ready to conduct future operations in a coordinated and highly synchronized manner with the Republic of Korea against the north in a crisis one of the officials said.

The two sides are discussing the final details of the reduced effort.

The first exercise involved is a so-called command post exercise scheduled to begin in the next several days. These types of exercises simulate the essential ability of top commanders and their senior staffs on both sides practicing precisely how they would operate together in a crisis. In the Republic of Korea, this is vital training as both sides would operate jointly in any combat crisis against North Korea.

It is not yet clear if any field exercises will be affected.

In Monday, US Defense Secretary Mark Esper only said the scale back was being considered but insisted it would not have a military impact. “I’m sure that we’ll remain fully ready to deal with any threats that we might face together,” Esper told reporters.

But US officials say when exercises are scaled back or cancelled — as they were in August 2018 — capabilities are particularly impacted because of the regularly scheduled high rate of changes in assignments for both nations forces. That can mean each year more than 50% of troops are replaced with newly assigned forces that may not have experience in commanding in Korea.

South Korea now has more than 970 cases of coronavirus.