At the end of January, chemists and engineers left Aberdeen Proving Ground for the Mediterranean Sea to lead the historic destruction of Syria's chemical weapons.

More than two months later, they're still waiting for the mission to start.

As the Syrian conflict lurches into a fifth bloody year, the forces of President Bashar Assad appear to have gained the advantage over U.S.-backed rebels. Assad's army, once dismissed as inadequately equipped, ill-prepared for guerrilla fighting and of suspect loyalty, has capitalized on infighting among the rebels and a steady flow of support from Moscow and Tehran to chalk up victory after victory.

Meanwhile, the agreed-upon destruction of Syria's chemical weapons — a rare positive development for the rebels and their Western backers — has been beset by delays.

After hundreds of civilians reportedly were killed in a chemical attack on a Damascus suburb last summer, Assad said he would surrender Syria's weapons stocks to be destroyed by an international team.

But amid fighting that has left more than 100,000 dead and displaced a quarter of the population, the regime has missed several deadlines to complete the delivery of the chemicals, putting the mission weeks behind schedule.

The Marylanders won't begin their shipboard operation to neutralize the most dangerous materials until they have the entire stockpile. With only about 40 percent of those chemicals now under international control, the head of the Organisation for the Prohibition of Chemical Weapons acknowledged recently that the June 30 deadline for their complete destruction could be in jeopardy.

The mission has been complicated further by tensions between its two principal architects — the United States and Russia — over Moscow's annexation of Crimea. Plans for a joint NATO-Russian operation to provide security for the U.S. container ship on which the Aberdeen team is to destroy the chemicals have been canceled.

In the meantime, some 64 civilian specialists from the Edgewood Area of Aberdeen Proving Ground — some of them now aboard the container ship MV Cape Ray at a naval station in Rota, Spain, others still in Maryland, awaiting orders — remain in limbo.

"The crews are ready. People are champing at the bit to go," said Jeffrey Harris, a civilian leader with the Pentagon's Joint Program Executive Office for Chemical and Biological Defense in Edgewood. "We're just waiting for Syria to hold up their end of the bargain."

Syrian officials agreed last year to transport chemicals from 12 sites to the Syrian port of Latakia, where they are being loaded onto cargo ships provided by Denmark and Norway. They have blamed delays in delivering the chemicals on security problems.

The Edgewood team, a mix of Army civilians and contractors associated with the Joint Program Executive Office and the Edgewood Chemical Biological Center, is waiting to destroy Syrian stocks of the World War I blister agent mustard and the sarin precursor DF.

When the Danish ship Ark Futura has received all of Syria's declared stocks of those chemicals — some 566 tons — it is to sail under heavy security to the Italian port of Gioia Tauro. There the materials are to be transferred to the Cape Ray.

The Marylanders are then to head out to international waters, where members are to neutralize the chemicals on equipment they developed in Maryland for the mission. The waste is to be taken to Germany and the United Kingdom for disposal.

The Edgewood specialists have decades of experience in destroying U.S. and other weapons stocks — but at highly secure and often remote facilities, on land, built for the purpose. Now, for the first time, they're planning to do the work aboard ship, on the open sea.

Leaders say safety, not speed, will be their priority. The work is expected to take between 60 and 120 days.

Ahmet Uzumcu, head of the Organisation for the Prohibition of Chemical Weapons, expressed optimism last month that the mission still could be completed on schedule.

"I think that some targets have not been met," he told reporters after meeting with Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov at the Hague. "But the deadline of 30 June still remains our target, and we think we can finish the destruction by that time, or close to that time."

Kerry said "real challenges" lie ahead.

"We in the United States are convinced that if Syria wanted to they could move faster," he said.