Fifty-five Royal Navy personnel on a Plymouth-based helicopter carrier have been screened for tuberculosis after two crew contracted the disease.
HMS Ocean can carry up to 1,270 servicemen
The navy is investigating two confirmed cases in two months on board HMS Ocean.
The Royal Navy said the first crewman, diagnosed in June, had recovered while the latest case was diagnosed on Wednesday and is being treated.
The ship is still operational but the outbreak has forced it to pull out of a visit by the Queen in London next week.
The source of the infection is not known, but it is understood both men worked in the marine engineering department. The ship has not been quarantined.
The MoD said the first crewman to develop the disease, an able seaman, was expected back at work soon.
The other diagnosed crewman was in hospital, the MoD said.
The Health Protection Agency is advising the navy on treating and controlling the disease.
The ship, currently in Portsmouth, is due to return to its Devonport base next week.
It was forced to pull out of a visit by the Queen after an onboard outbreak when berthed at Greenwich Pier in south-east London. She was due to mark the 250th anniversary of the Marine Society.
The Royal Navy said not hosting the event was an "enormous disappointment" for HMS Ocean's crew.
Amphibious assault vessel HMS Albion will host next Friday's celebration instead.
Devonport-based HMS Ocean is one of the three largest ships in the British fleet, alongside aircraft carriers Invincible and Illustrious. She can carry up to 1,270 servicemen.