A naval ship with a 100-bed medical complex and loaded with helicopters, landing craft, tonnes of emergency supplies and almost 400 personnel is preparing to head for Sierra Leone to help tackle the Ebola crisis.

Royal Fleet Auxiliary Argus, a vast hospital and support vessel, will sail from Falmouth in Cornwall to west Africa and act as a forward base for army medics, engineers, soldiers and aid experts who will build and operate medical centres, train local doctors and nurses and transport vital supplies.

By the end of next month 750 British troops will be operating in Sierra Leone. With troops continuing to withdraw from Afghanistan it will be the largest overseas deployment of UK forces anywhere in the world.

During a visit to the 28,000-tonne RFA Argus the defence secretary, Michael Fallon, described the ship, which first saw action during the Falklands conflict, as a “warhorse” embarking on a vital humanitarian mission.

Fallon said British efforts in west Africa would help save lives there but also stop Ebola spreading through other parts of the continent, Europe and the UK. “She will be at the frontline defending Britain against the disease,” he said.

“We’re doing more than any other country, certainly much more than in Europe. We’re putting a huge effort into this.”

While Fallon spoke on the flight deck of the 175-metre-long ship, military and civilian staff (85 of the 140-strong ship’s crew are non-military) loaded supplies, weaponry and equipment – including protective suits – on the ship ahead of her departure at high tide on Friday.

The ship’s commanding officer Captain David Eagles, a veteran of conflicts in the Middle East and the Balkans, accepted there was an “unknown quantity” to this mission. “It is worrying to the crew and their families but I’m confident we can achieve what we’ve been tasked to do and bring all our people safely home to their families.”

Argus has varied roles. First, she will transport personnel and hardware, including more than 50 vehicles along with tonnes of bottled water and ration packs. The voyage, which includes a stop-off in Gibraltar to pick up more gear, will take about a week.

When in theatre, she will act as a base for three Royal Navy Merlin helicopters, which will be used in surveillance work and to move equipment and people around. Anti-submarine warfare equipment is being stripped out of the aircraft to provide more space. The ship has its own mini air traffic control centre, Flyco.

Argus will also become a giant landing stage for powerful boats operated by 80 Royal Marines, who will provide the security for the British operation.

Finally the ship, which has the same sort of facilities available as at an NHS hospital, will provide medical cover to British personnel – military and civilian – who might suffer injury or illness while working in Sierra Leone.

About 80 medical staff will be on board, including surgeons, consultants, radiographers, anaesthetists and nurses. Some will go on shore to help with the training; others will remain on Argus.

What the ship will not do is treat anyone who contracts Ebola. Every time a marine or medic goes on shore, he or she will be asked to fill in a questionnaire about contacts with local people. If they have had contact, their temperature will be taken twice a day and if there are concerns that they have Ebola they will be evacuated to a British-run facility onshore.

The idea is to keep the ship a safe, sterile environment from which the UK’s efforts can be coordinated locally.

on Tuesday 120 members of the ship’s company gathered in the canteen to hear a 90-minute briefing on Ebola.

Dr Ruth Howlett-Shipley, the Royal Navy’s public health consultant, told them: “We are doing everything we can to make sure that you go out safely and come back safely.” Among the questions she faced was: “If I sit next to a marine at breakfast, who shook hands with an infected person, will I contract Ebola?”

Surgeon Lieutenant Dan Hawkins, the medical officer for Argus, said: “There’s always concerns when you deploy and with the nature of where we’re going to there are added concerns and considerations but the crew are very much looking forward to going.”

Conditions on board will vary. Some of the men in the so-called austere accommodation will sleep in 27-person dormitories; others share smaller cabins. Some will leave the vessel on missions but those who have no operational reason to head for shore will stay on board for the whole of a two- or three-month tour. They have Sky Sports and a ration of two cans of beer a day.

It will not be a short trip – Argus has been told to prepare for six months away. Captain Eagles said the crew, medics and troops were used to working in trying conditions. “It will be quite tough but I think people will understand. I think people are going to be quite busy.”