WASHINGTON — Two collisions between Navy destroyers and commercial vessels in the Western Pacific earlier this year were “avoidable” and the result of a string of crew and basic navigational errors, the Navy’s top officer said in reports made public on Wednesday.

Seven sailors were killed in June when the destroyer Fitzgerald collided with a container ship near Japan. The collision in August of the John S. McCain — another destroyer, named after Senator John McCain’s father and grandfather — and an oil tanker while approaching Singapore left 10 sailors dead.

In the case of the Fitzgerald, the Navy determined in its latest reports that the crew and leadership on board failed to plan for safety, to adhere to sound navigation practices, to carry out basic watch practices, to properly use available navigation tools, and to respond effectively in a crisis.

“Many of the decisions made that led to this incident were the result of poor judgment and decision making of the commanding officer,” the report concluded. “That said, no single person bears full responsibility for this incident. The crew was unprepared for the situation in which they found themselves through a lack of preparation, ineffective command and control, and deficiencies in training and preparations for navigation.”

In the case of the John S. McCain, the investigation concluded that the collision resulted from “a loss of situational awareness” while responding to mistakes in the operation of the ship’s steering and propulsion system while in highly trafficked waters.

“The collisions were avoidable,” Adm. John Richardson, the chief of naval operations, said in a summary of the two reports, released by the Navy on Wednesday morning.

The release of the twin reports on the collisions came a day after the Navy held closed-door briefings for lawmakers on Capitol Hill on its findings and recommendations, and sent officers crisscrossing the country to brief family members of the sailors killed. A broader review of the Seventh Fleet’s pace of operations, training, equipment and maintenance is to be released on Thursday.

Senator Roger Wicker, a Republican from Mississippi, attributed the two fatal collisions to dwindling Navy resources in the Pacific, combined with judgment and training errors — a sentiment echoed by lawmakers as they left Tuesday’s private hearing.

“In general, we’re asking too few ships to do too many things,” Mr. Wicker said.

Mr. McCain, Republican of Arizona and chairman of the Senate Armed Services Committee, on Tuesday also pointed to the automatic budget cuts on the Pentagon since 2013, known as sequestration, as one of the primary culprits behind the combined 17 deaths aboard the two destroyers.

“We’ve deprived them of the funds to do it,” Mr. McCain said of the continuous operations in the Pacific. “We’re putting those men and women in harm’s way to be wounded or killed because we refuse to give them the sufficient training and equipment and readiness. It’s a failure of Congress. It’s on us.”

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Already the fallout from the two fatal crashes as well as two others in the western Pacific this year, has been dramatic.

The commander of the Navy’s Pacific Fleet, Adm. Scott H. Swift, took early retirement after being notified that he was no longer in the running to take charge of the Pentagon’s overall Pacific Command, which would oversee any military operations against North Korea.

Vice Adm. Joseph P. Aucoin, the former head of the Seventh Fleet, based in Japan and the Navy’s largest overseas, was removed in connection with the accidents. The Navy’s top officer for ships worldwide, Vice Adm. Thomas S. Rowden, has also said he will retire early.

Several other senior officers in the Seventh Fleet chain of command, as well as the commanding officers of the Fitzgerald and John S. McCain, have also been relieved of their duties.

Even before the more comprehensive review was conducted by Adm. Phil Davidson, the head of the Fleet Forces Command in Norfolk, Va., urgent new orders went out in early September for United States Navy warships.

These directives included more sleep and no more 100-hour workweeks for sailors. Ships steaming in crowded waters like those near Singapore and Tokyo were ordered to broadcast their positions as do other vessels. And ships whose crews lack basic seamanship certification will probably stay in port until the problems are fixed.

These were all seemingly obvious standards, military officials said, except that the Navy rushed the remedies into effect only after the two deadly collisions in two months, despite repeated warnings about the looming problems from congressional watchdogs and the Navy’s own experts dating to 2010.