Members of South Korea‘s virus-hit Cheonghae naval unit returned home from Africa on Tuesday, the defense ministry said, after cutting short their anti-piracy mission following an unprecedented mass outbreak that infected 247, or 82 percent, of the 301-member unit.

One of two KC-330 Cygnus multirole aircraft dispatched to airlift all of the troops returned to an air base south of Seoul at 5:30 p.m., carrying 160 infected members, including 16 who had been treated at local hospitals.

The second plane carrying the remaining 141 members, including 87 patients, arrived at 6:20 p.m., according to the ministry.

“Fourteen individuals, including three showing moderate symptoms, will be transferred to medical institutions,” the ministry said in a statement.

Buses and ambulances transferred the members to military hospitals and treatment centers where they were to undergo another round of virus tests.

Defense Minister Suh Wook and other senior military officials were also at the airport to receive the returning troops.

Depending on the test results, confirmed patients will receive treatment while those who test negative will be transferred to the military’s quarantine facilities, the ministry said.

Six cases were first identified Thursday and subsequent tests on all of the members confirmed the mass outbreak on their 4,400-ton Munmu the Great destroyer. Poor initial responses were blamed, such as giving only cold medicine to a sailor who first developed symptoms early this month.

The number of infections could further rise considering the virus‘ incubation period. The military earlier said 50 have tested negative and the samples of four individuals were undecipherable.

None of the troops had been vaccinated as they left South Korea in early February, just before the country began its inoculation campaign.

Defense Minister Suh issued an apology over the mass outbreak earlier in the day, admitting insufficiency in efforts to vaccinate the sailors.

“As the defense minister, I feel a heavy responsibility, and I extend deep apologies to the members of the Cheonghae unit, their families and the public,” he said.

Their destroyer will be piloted back home by a team of about 150 sailors who flew there on the aerial tankers.

The return of the 34th contingent is about a month ahead of the original schedule, marking the first early return of a contingent since the unit was first deployed in 2009.

The troops are rotated every six months for an anti-piracy mission in the Gulf of Aden off the coast of Somalia and around the Strait of Hormuz.

A replacement contingent has arrived at the mission area and begun operations, according to officials. Most of the members of the new batch received COVID-19 vaccines before their departure.

The mass outbreak marked the worst-ever cluster infection among service members since the military reported its first coronavirus case in February last year.

The infections appear to have begun after the vessel was docked at an African port from June 28-July 1 to load supplies.

One sailor showed symptoms of a cold a day after the destroyer left the port. But he was found to have been given only cold medicine without undergoing a virus test.

Amid mounting criticism over the military’s failure to provide vaccines to the unit members, the defense ministry said the unit was not subject to COVID-19 vaccines provided to United Nations personnel on peacekeeping missions as it is under a separate multinational task force.

The ministry also said the country where the Cheonghae unit often makes port of call does not allow vaccination on foreign military personnel.

Still, President Moon Jae-in said Tuesday it is hard for the government to avoid criticism that its relevant measures were “insufficient,” urging officials to thoroughly handle the issue.