WASHINGTON — The numbers are staggering.

More than 210,000 illegal migrants crossed the central and eastern Mediterranean in 2014, according to Frontex, the agency that coordinates border movements in Europe. More than 150,000 migrants were rescued at sea between October 2013 and September 2014, according to the Italian government, and more than 3,000 died. Another 2,200 migrants were rescued between Italy and Sicily on Feb. 12. More than 11,000 were rescued between April 12 and 18. On May 2 and 3 more than 5,800 were picked up.

These are just a few examples — there are many more. They reflect a growing crisis that European nations aren't designed to handle, and ones they're scrambling to respond to, at great cost and political consequence.

The greatest share of rescue operations cited above were handled by Italian government ships; Navy, Coast Guard, Border Patrol and Customs Service vessels. Using destroyers, frigates, corvettes, patrol craft and even submarines, Italy's sea services have become the busiest and hardest-working such force in the world, bearing the brunt of the rescue and interdiction operations.

But the Italian government, fed up with the monthly €9 million (US $10.1 million) bill for rescue operations with little help from the rest of Europe, called a halt to the operations in mid-April. Just days later, on April 19, about 750 migrants drowned when their craft sank.

At an emergency summit meeting in Brussels on April 23, European Union (EU) leaders pledged to greatly expand support and committed to send more naval and coast guard units. They also tripled the budget for migrant patrols.

Frontex reported on May 26 that the European Commission will soon provide an additional €26 million to strengthen Operation Triton in Italy and Poseidon Sea in Greece from June 2015 until the end of the year. The budget for Triton for this year will stand at €38 million and €18 million for Poseidon Sea. Next year, the European Commission will provide Frontex with an additional €45 million for the two operations.

With the new agreement, 26 nations are now engaged in migrant patrols in the Mediterranean. Britain deployed its largest warship, the amphibious ship Bulwark, which on May 7 picked up its first 110 migrants spotted aboard a rubber boat. Bulwark used its landing craft to transfer the refugees to an Italian Coast Guard vessel.

A day later, the German frigate Hessen picked up about 200 migrants from a leaky wooden vessel, and the German naval supply ship Berlin rescued 180 refugees off the Libyan coast.

Naval forces far outside the Med are converging to join the task, too, including patrol vessels from Ireland and Iceland.

But the factors driving the migrations are showing no sign of slowing down — quite the contrary, warn numerous human rights groups.

"There are about 10 times the number of deaths at sea this year versus last year," said Robert Gramer, assistant director of the Transatlantic Security Initiative with the Atlantic Council. "Those numbers will climb as the temperature climbs.

"This isn't going to go away," he added. "I would see the number of migrants coming over to Europe increasing exponentially."

Frontex reported that for the three days of May 29 to 31, more than 5,000 migrants were saved in the central Mediterranean. British, Maltese, Belgian and Italian vessels, along with Icelandic and Finnish aircraft, took part in the rescue effort.

"This is the biggest wave of migrants we have seen in 2015," Frontex Executive Director Fabrice Legger said in a press release.

Where They're Coming From

The largest groups of refugees come from Syria and Eritrea, more than 32,500 each in 2014, according to the Italian government. Smaller numbers come from Mali, Nigeria, Gambia, Palestine and Somalia. With continuing military gains by the Islamic State in Syria and Iraq and no end in sight for the civil war in Syria, there is no letup.

Elsewhere in the world, naval forces are engaged in refugee or migrant interdiction on a continuing basis. Outside the Mediterranean, the most active area of migrant activity is in the Andaman Sea, where Bangladeshis, and Rohingya Muslims from Myanmar, are fleeing, headed for Indonesia, Malaysia and Thailand.

Media reports indicate thousands of refugees are at sea in south Asian waters, denied permission to land and with nowhere to refuel or replenish. Those reports also indicate more than 4,600 refugees came ashore in southeast Asian territory in recent weeks.

Just last week, Thailand sent seven naval ships into the Andaman Sea to interdict migrant ships. The navies of Indonesia, Malaysia and Myanmar are all undertaking rescue or interdiction operations. Australia's Navy, meanwhile, is executing the government's controversial turn-away policy, begun in 2013, with seaborne patrols refusing to allow migrant vessels to reach shore. The BBC reported that in 2013 some 300 boats with more than 20,000 migrants got to Australia, while in 2014 only one vessel reached the country.

While the situations in the Mediterranean and South Asia continue, surge operations like those in Yemen also draw in warships for rescue roles they are not designed for. Numerous naval warships and support ships from several nations have embarked refugees from Yemen since late March. The effort includes naval ships from China, France, India, Iran, Pakistan, Russia, Saudi Arabia and the US. Destroyers, frigates and patrol vessels were among the participating naval units.

The Right Ship for The Job

With all these gray-hulled naval ships and white-hulled coast guard vessels drawn away from their normal duties, are these the best types of ships to assign to the mission?

"Warships have a whole bunch of things that make them relevant and very helpful in these kinds of operations — sustainability, helicopters, great radars, great command and control facilities," said Eric Thompson, the director of strategic studies at the Center for Naval Analyses in Washington. "They usually have small boats and boarding capabilities, they have safety equipment. Those are all good things.

"But on the down side, they're configured through and through for a couple things that make them not particularly well suited – berthing is designed for the complement of people that actually engage in fighting the ship," Thompson said.

"Medical personnel are one, two, three people — medics, not really doctors. They don't have surgical facilities, quarantine facilities. The potable water and the food throughput is designed for the crew complement. There aren't a lot of open spaces in these ships where you can put people, cots, heads [bathrooms]."

Naval ships also are not configured to easily pick people up from the water, noted Jerry Hendrix, an analyst with the Center for a New American Security in Washington and a former director of naval history for the US Navy. The high sides of warships make access difficult, he pointed out. "It's not good to bring people up and down."

Thompson agreed. "Getting people on and off these ships can be an undertaking, they're not designed for it. Pulling people from the sea onto a ship is not a simple undertaking. There are a lot of ships that don't do that very well."

New American ship designs like the littoral combat ship (LCS) and joint high speed vessel (JHSV) might also be suitable for sustained migrant rescue missions, but no other nation has them.

"Given these challenges, foreign nations might want to take another look at US ship design," Hendrix noted, "specifically both LCS variants and JHSV, due to their large cavernous mission bays and their ability to provide space for people on board."

Amphibious ships with large well decks are well suited to rescue and humanitarian missions — American amphibs often take part in relief missions — but while the US has 30 such ships, most nations have far fewer, often only one or two.

Other navies are buying combat ships with built-in features to enable more expeditionary or humanitarian roles.

Italy is building the Pattugliatore Polivalente D'Altura (PPA), or Offshore Polyvalent Patrol ship, a 4,500-ton, frigate-sized vessel with a modular design that can be enhanced for relief and humanitarian missions.

The ships will have a central zone that will be able to host vehicles or cargo containers, while space under the flight deck is designed to host a temporary hospital facility, anti-pollution equipment or special operations equipment. The vessel will be able to supply power and water for 6,000 people ashore.

"But the PPA program was in the works before the migrant crisis erupted, so those requirements were already there" observed Gramer. "But they're great for modularity, and can be fitted for rescue or fighting."

The US Coast Guard has long experience in migrant interdiction, particularly in the Caribbean region, and a requirement was included in its National Security Cutters to be able to handle large numbers of people without threatening the security of the ship. The vessels are fitted with an embarkation station close to the waterline so people can come aboard with relative ease, and feature enclosed passageways able to temporarily shelter large numbers of people without letting them into the ship's inner areas, where access to engine rooms, command and control spaces and weapons could prove a security risk.

New cutters, including the Fast Response Cutters (FRC) and the future Offshore Patrol Vessel, also feature stern ramps, a key rescue feature, said one former service chief.

"The cutters have the stern-launched ability to get people on board quickly and safely in almost any kind of sea state," said retired Adm. Jim Loy, a former director of Homeland Security and Coast Guard Commandant from 1998 to 2002, the time when the new cutter requirements were being drawn up.

"The FRC has a watertight boarding access virtually at the water's edge, as opposed to having to pull refugees out of the water by yanking them over lifelines," Loy said. The features make it far easier to bring people on board, even in turbulent sea states.

Loy noted that most warships "are designed to be successful at what they hope never happens" — combat. But for missions such as rescue at sea, "give me a Coast Guard platform to meet our missions — the design and the training of people — as opposed to Navy platforms."

With designs such as the PPA and Germany's F125 frigates, there already is evidence navies are thinking of combatant ships in more expeditionary roles. Still to be seen is whether long-term migrant interdiction and rescue capabilities are introduced into requirements documents.

"Is this something that navies are going to have to alter force structure for? That's a long-term investment issue that signals a sea change in naval architecture," said Hendrix.

Tom Kington in Rome contributed to this story.