Last week, an Argentine navy submarine apparently suffered a malfunction and went missing off the coast of South America. Within hours, ships, planes, and submersibles from Argentina, Chile, Brazil, the United Kingdom, and the United States converged on the area.

The world's navies have developed sophisticated undersea rescue procedures since submarines entered widespread use in the years before World War I. But time and the weather are working against international efforts to find the ARA San Juan and attempt to rescue her 44 crew members.

"There are 20-foot waves," Eric Wertheim, an independent naval analyst and author of Combat Fleets of the World, told me. "It's really bad. But the real problem is, a lot of the window is passing. Each hour that goes by, the chance of a successful outcome dwindles."

The 216-foot-long, torpedo-armed San Juan is the pride of the Argentine navy. Buenos Aires acquired the vessel from Germany in 1985. San Juan had recently undergone modernization and was reportedly sailing along the edge of South America's continental shelf, where the water is thousands of feet deep, when something went wrong. Naval officials lost contact with the vessel on November 15.

“What we interpret is that there must have been a serious problem with the communications [infrastructure] or with the electrical supply, cables, antennae or other equipment,” Argentine navy spokesman Enrique Balbi said.

The Argentine navy said San Juan was carrying emergency supplies of food, water and oxygen. But it's unclear how long the air aboard the submarine might remain breathable if the vessel is fully submerged.

A dozen rescue vessels spent the weekend criss-crossing the search zone, searching via sonar, as aircraft, including two US Navy P-8s and a NASA P-3, flew overhead. Some patrol planes carry equipment that can detect the magnetic signature of a sub’s hull. US Air Force C-17 and C-5 cargo planes hauled two Navy rescue chambers and a pair of underwater surveillance drones to the region.

One chamber, the World War II-vintage Submarine Rescue Chamber, can descend as deep as 850 feet below the ocean's surface and rescue six sailors at a time. The newer Pressurized Rescue Module can dive 2,000 feet and fit 16 sailors. Both chambers are operated by two-person crews.

Pressurized Rescue Module (PRM-1) Falcon, part of the submarine rescue diving and recompression system. Image: US Navy

But the chambers are useless until rescue forces actually locate San Juan, whose hull can withstand pressures at depths up to 1,000 feet. As the wind and waves worsened over the weekend, the chances of even finding the sub dwindled. "The weather is very challenging for naval operations," Wertheim said. And submarines are, by design, hard to find.

Submariners are trained to respond to catastrophic malfunctions, but they know that chances of survival can be slim. "There are procedures, we read them and trained on them, but I never really got the impression that many submariners expect to survive sinking," Cleve Langdale, a former US Navy sub crewman, told me.

Pope Francis, a native of Argentina, offered "fervent prayers for the 44 officers aboard the ARA San Juan." Rescuers have the planes, ships, and submersibles to retrieve the Argentine sailors, if they're still alive. What rescue crews need is calm weather—and any hint at all of the submarine's location.