WASHINGTON — The Navy’s top officer on Monday ordered a pause in operations for operations around the world in the wake of the second major collision in three months of one of its front-line combat ships.

Adm. John Richardson, the Chief of Naval Operations, said in a video that the pause was ordered to allow commanders to take immediate action to keep sailors and ships safe

Richardson said the latest collision involving the USS John S. McCain had left him “devastated and heartbroken.”

On Sunday, the McCain, a guided-missile destroyer, collided with an oil tanker east of the busy Straits of Malacca and Singapore on Sunday. Ten sailors remain missing, and five were injured in the latest of four major mishaps involving ships in the Navy’s 7th Fleet.

More: Commander and leadership of stricken destroyer Fitzgerald to be relieved for collision

On June 17, the USS Fitzgerald, badly damaged in a collision on June 17 that killed seven sailors off the coast of Japan.

Richardson also ordered a Navy-wide review to get at the “root causes” of the problems.

The review will be done on a “very tight timeline” because of the need for urgent action.

“We need to get to the bottom of this,” Richardson said. “So let’s get to it.”

Richardson told reporters at the Pentagon on Monday that the second “extremely serious incident” in little more than two months “gives great cause for concern that there is something out there that we’re not getting at.”

The McCain is moored in Singapore, while search-and-rescue operations continue.

Top priority missions, such as ballistic missile defense due to tensions with North Korea, will likely continue despite the pause, said Bryan Clark, a senior fellow at the non-partisan Center for Strategic and Budgetary Assessments, Navy veteran and fpr,er senior civilian official at the Pentagon.

Commanders and crews elsewhere will examine training plans and how prepared sailors are before they’re deployed, Clark said.

Since 2000, the Navy’s fleet has shrunk but demand for ships at sea around the world has risen, Clark said. That mismatch means sailors and ships are stressed.

“Each ship is working 20% more,” Clark said.

There are 11 cruisers and destroyers, including the Fitzgerald and McCain, based in Japan, Clark said. Their temporary loss for repair will increase the workload on the remainder of the ships in the western Pacific. The Fitzgerald must be piggybacked on a larger ship and sailed back to the United States to be made seaworthy.

Ships based in Hawaii or the United States will likely be called on for longer-than-normal deployments to replace them, he said.

Separately, the Navy will investigate why the collisions occurred. Last week, Navy leaders concluded that sailors on the bridge of the Fitzgerald had “lost situational awareness,” leading to the crash with much larger cargo ship. The ships top two officers and enlisted sailor were relieved.

The initial report on the Fitzgerald showed that sailors asleep in their berthing compartment below the water line had only minutes to escape. Water gushed through the 13-by-17 foot gash, flooding the area with seawater that was neck high within two minutes. The ship’s list, and floating debris, hindered escape. The sailors who died were closest to the rupture in the hull.

Ill-defined shipping lanes

The accidents involving the McCain and Fitzgerald took place in congested seas with lots of shipping traffic, Clark said. The shipping lanes are not well defined.

“It’s like the on-ramp to a freeway,” he said. “There’s lots of traffic coming from different directions.”

It’s incumbent on U.S. Navy ships with sophisticated navigation systems, sensors and trained crews to sort out the confusion and take advantage of their advantage of speed and maneuverability to avoid collisions with lumbering cargo vessels, Clark said.

Meanwhile, the investigation on the alarming frequency of the crashes and other mishaps will likely focus on shortfalls in personnel and training.

In May, the Government Accountability Office warned that the Navy needed to ensure that its ships had enough sailors with the required skills to operate safely and effectively. One problem, the GAO noted, dates to 2001 when the Navy embarked on a plan called “optimal manning,” which sought to reduce the cost of personnel. In 2010, the Navy concluded that the program had damaged the readiness of crews.

The problem is expected to get worse as the Navy embarks on a plan to grow its fleet, according to the GAO.

“The fleet is projected to grow from its current 274 ships to as many as 355 ships, but the Navy has not determined how many personnel will need to be added to man those ships,” the GAO concluded.