The Ministry of National Defense has launched a sweeping inspection into the massive COVID-19 outbreak that forced its unvaccinated anti-piracy unit to return home five months after departing for Africa, military officials said Thursday.

The inspection comes amid mounting calls for Defense Minister Suh Wook to step down to take responsibility for an aborted overseas mission, a first for the military, which airlifted the 301-strong Cheonghae Unit on Tuesday. More than two-thirds of the crew returned home infected.

The seamen were found to have been initially omitted from the vaccine priority list because of supply constraints. And they were overlooked again later, when the military expanded its vaccination campaign with US-provided Johnson & Johnson vaccines.

The military said the reason was that the seamen could not handle a possible allergic reaction to the vaccine or manage the extreme storage conditions for the vaccine onboard. Critics have said the military could have enlisted help from the nearby US Navy or from local authorities.

Along with the Joint Chiefs of Staff, the Navy, Armed Forces Medical Command and the ministry itself, Cheonghae, whose tally of infections rose to 271 on the second round of tests done here, will face scrutiny over its decision to pack COVID-19 antibody tests, which take longer to detect infections than antigen tests.

“We will look into whether all the people there did exactly what they were supposed to. We will also see if they could have done it better,” a ministry official said, adding the inspection will look into what triggered the outbreak aboard the 4,400-ton destroyer, which is on its way back home.

The military suspects the outbreak started on July 2, a day after the destroyer left a nearby port where it had made a four-day supply stop. A military cook first exhibited COVID-19 symptoms, followed by others. But medical staff onboard allegedly determined they had a cold, disregarding evidence demonstrating otherwise.

Vice Defense Minister Park Jae-min said the military will see if the staff had made the right call, without elaborating on the controversial decision critics have labeled poor decision-making that led to the worst military outbreak since the pandemic started in January last year.

No seamen reportedly had come into any suspicious contact with local people who helped them to load supplies onto the ship. Nor had any crew member gone AWOL, according to Park. But he noted the ministry is still looking for conclusive evidence.

Of the 271 infected personnel, 17 were hospitalized and one was severely ill. The rest have been placed in COVID-19 treatment centers, with those who tested negative in quarantine until the incubation period runs out.

The ministry said the two-week inspection, which is scheduled until Aug. 6, could go longer if necessary.