Migrant rescue ship preparing for the worst

But a closer look tells a larger story of a disaster that saw some 130 perish in a shipwreck in late April.

On the bridge, SOS Mediterranee's rescue coordinator Luisa Albera scrolls the mouse across the monitor.

"All of these were alerts," she said on Thursday (24 June), pointing to at least two dozen marks that also represented rescues.

Some are shaped like stars or squares and others like circles.

In a separate screen capture two purple circles stand out. The mark indicates what would later turn out to be a massive loss of life, described by Pope Francis as a "moment of shame".

EU commissioner Ylva Johansson called it a "European tragedy."

Ocean Viking had only been a few days at sea when it arrived in the aftermath of the drownings.

After receiving an alert, it coordinated a rescue operation in storm conditions with three other commercial vessels in an area spanning 57km wide and 40km long.

The first bodies were found by Rose, the name of one of the commercial vessels. Many others were lost to the sea.

The fear of another similar experience remains a stark reality for its crew of mixed nationalities in the days and weeks ahead.

The number of people that have attempted to cross the central Mediterranean in the first five months has increased by 151 percent when compared to the same period last year. Almost 4,200 tried to cross in May alone, according to the EU's border agency Frontex.

On Thursday evening in Brussels, EU heads of state and leaders agreed to better coordinate on search and rescue as part of a larger effort to "prevent loss of life and to reduce pressure on European borders."

But their focus will remain on securing bilateral deals with countries outside Europe to prevent people from taking the journey in the first place. It is a priority, they said, instructing the European Commission "to immediately reinforce concrete actions" with countries of origin.

It means charity rescue operations will have to remain vigilant for the foreseeable future.

'You will not be returned to Libya'

On deck at a port in Marseille, the crew are hoisting in large containers, crates, and boxes of supplies as the ship readies for a new departure.

Others are securing and fastening the three rescue speed boats, also known as Rigid Hull Inflatable Boat or Rhibs.

Onboard, the crew is passing boxes over boxes of food supplies, over the deck and into the galley and storage units further in the belly of the boat.

Outside and on the stern of the ship are several large open containers. One stores 1,000 life jackets.

Others are reserved as shelters for adult male survivors. "You will not be returned to Libya," a notice on the inside wall says in English, French, and Arabic.

Behind the male-only shelters is a mini-hospital, stocked with medical supplies and four beds for the sick and injured.

Some of those rescued may have to be treated for a wide range of illnesses.

Some will have been tortured, left with festering wounds and possibly even broken limbs, says one of the medical staff.

The medical team also includes a midwife, with her own equipment and room to tend to any possible future mothers.

It has not happened yet onboard the Ocean Viking. But the Aquarius, predecessor vessel of the Ocean Viking, had delivered six.

The ship is due to set sail in the next few days.