Gene R. La Rocque, retired Navy admiral who became a critic of the Pentagon. (Family photo)

Gene R. La Rocque, a retired Navy rear admiral who witnessed the Japanese attack at Pearl Harbor in 1941 and who later irritated many former colleagues with his outspoken criticism of Pentagon practices and what he considered a suicidal nuclear arms race, died Oct. 31 at a hospital in Washington. He was 98.

The cause was kidney failure, said his daughter, Annette La Rocque Fitzsimmons.

Adm. La Rocque (pronounced la-ROCK) joined the Navy in 1940, served in the Pacific throughout World War II and rose to the rank of two-star admiral, or rear admiral upper half.

During the 1960s, he became one of the top strategic planners for the Joint Chiefs of Staff at the Pentagon. In 1968, he was sent to Vietnam to assess the conduct of the war and turned in a critical report questioning the U.S. mission in Indochina.

“Fundamentally,” he said in a 1986 profile in the New Yorker magazine, “I couldn’t find anyone to tell me why the United States was in Vietnam and what it was we were trying to accomplish.”

Adm. La Rocque’s analysis made him persona non grata at the Pentagon — “It was easier to keep the war going than to say ‘call it off’ ” — and he was passed over for promotion. When he retired from the Navy in 1972, he founded the Center for Defense Information, one of the first independent organizations relying on retired military officers to analyze defense policy with a skeptical eye.

Adm. La Rocque, who was later joined by retired Rear Adm. Eugene Carroll, guided CDI for more than three decades. The group accepted no contributions from the government or from defense-related companies.

Its widely read newsletter, Defense Monitor, exposed excessive spending by the Pentagon and highlighted programs and weapon systems that Adm. La Rocque considered wasteful or unnecessary. He often pointed out that the military used to manufacture its own weapons rather than rely on profit-motivated defense contractors.

His views made him one of the favorite military figures of liberal lawmakers on Capitol Hill, and he was a frequent presence on television and in the media. His larger goal, however, was to speak out against the threat of nuclear annihilation. He called for the dissolution of NATO and the Soviet-dominated Warsaw Pact and advocated for greater cooperation in science and culture.

“There are, unfortunately, some in the United States who believe that the Soviets are the enemy that we must defeat by war,” he told the New Yorker. “I think the enemy is nuclear war.”

Adm. La Rocque’s organization was the first to publish a reliable estimate of the number of nuclear warheads stockpiled by the United States and the Soviet Union: 50,000. When he appeared on Soviet television in 1983, saying the administration of President Ronald Reagan supported a large U.S. military buildup, the fallout from the defense establishment was immediate.

He was hardly divulging state secrets, but more than 500 retired admirals took out a full-page advertisement in the Washington Times condemning CDI and Adm. La Rocque (and misspelling his name in the process). His former boss, onetime Chief of Naval Operations Elmo R. Zumwalt, said, “I believe that if La Rocque’s ideas prevail my children will not live out their lives in freedom.”

When both men testified at a congressional hearing in 1985, Zumwalt refused to shake Adm. La Rocque’s hand.

When Adm. La Rocque was still in uniform, the Navy often sent him to schools, where he spoke of the harsh reality of war, drawing on his experiences in World War II.

“I told them it’s just a miserable, ugly business,” he told oral historian Studs Terkel for his 1984 book “The Good War.”

Adm. La Rocque was aboard the destroyer USS Macdonough at Pearl Harbor when Japanese airplanes attacked on Dec. 7, 1941. He spent four years aboard ships in the Pacific and took part in many battles, sometimes going ashore with a rifle and sidearm.

After the war, Adm. La Rocque threw away many of his military mementos. He wouldn’t watch movies about World War II.

“I hate to hear someone say, ‘He gave his life for his country’ — I don’t believe it,” he said in 1986. “It’s the country that takes life away from these kids in the name of honor and glory.”

Gene Robert La Rocque was born June 29, 1918, in Kankakee, Ill. His father, a car dealer who lost his business during the Depression, later ran a furniture store.

Adm. La Rocque studied at the University of Illinois but left to join the Navy shortly before graduating in 1940. He received a bachelor’s in 1963 from George Washington University and a master’s in international affairs from Georgetown University.

After his service with the Joint Chiefs, Adm. La Rocque was shifted to the Navy’s Pan-American Naval Affairs office, and he spent his final three years in uniform as director of the Inter-American Defense College at Fort McNair in Washington.

Despite his repeated clashes with Pentagon brass, Adm. La Rocque was invited to speak to U.S. service academies and the United Nations. He continued to lead CDI until the mid-2000s. The organization merged with the Project on Government Oversight in 2012.

His first wife, the former Sarah “Sally” Fox, died in 1978 after 32 years of marriage. His second wife, Lili Kerekes Danchik, died in 1994 after 14 years of marriage.

Survivors include three children from his first marriage, John C. La Rocque of Ashburn, Va., James C. La Rocque of Suffolk, Va., and Annette La Rocque Fitzsimmons of Woodstock, Va.; two stepsons; six grandchildren; and a great-grandson.

After founding CDI, Adm. La Rocque learned that his forthright views of the country’s military practices earned him a spot on one of President Richard M. Nixon’s enemies lists.

“It may be that the phones in my office are tapped,” he told the New Yorker. “I sincerely hope they are. I’m very anxious to get everything we know to the White House and to Congress, even if it has to be done through wiretaps.”