Seventy years ago today a U.S. Army Air Forces B-29 29 Superfortress Bockscar piloted by Major Charles W. Sweeney dropped a 10-foot long, 5-foot wide bomb containing more than 13 pounds of highly enriched plutonium over the city of Nagasaki, Japan.

The bomb — nicknamed "Fat Man" because of its squat shape — produced an enormous, fiery explosion equivalent to 21,000 pounds of TNT that instantly incinerated tens of thousands of civilians.

It was the last time an atomic bomb was used in warfare.

The horror of Nagasaki and Hiroshima, where three days earlier the world's first atomic bomb, nicknamed "Little Boy," also killed tens of thousands — within a month a total of about a quarter million in the two cities perished from burns, radiation poisoning and injuries; countless others later died from cancer  — has managed to serve all these years as a grim yet effective deterrent against future use of such awful devices.

President Harry S Truman, who ordered the 1945 bombings on Japan in order to shorten World War II and limit U.S. casualties that would have resulted from a ground invasion, was tempted but decided against using nuclear weapons against North Korea in 1951. Although nuclear weapons have since spread around the globe, no other nation has deployed them.

In the decades following World War II the United States and Soviet Union built up their stockpiles, as did other nations, and by the mid-1980s the number of nuclear weapons swelled to about 50,000. With various non-proliferation treaties that figure has dropped to about 15,000 today — still an overwhelming number that could annihilate the human race and all other living things many times over.

In addition to the United States and Russia, the nations that have nuclear weapons include the United Kingdom, France, China, India, Pakistan, Israel and North Korea.

Now we are poised to ensure that Iran doesn't join that exclusive club.

The Day continues to support the deal the Obama  Administration negotiated with Iran to curb that country's nuclear program in exchange for relaxed economic sanctions, and urges Congress to approve it after returning from recess next month.

We recognize concerns raised by Israel and congressional Republicans that Iran, which has had a long, contentious relationship with this country, cannot always be trusted but feel confident that safeguards and regular inspections will force it to comply with terms of the accord, if for no other reason than that it needs the money now being withheld because of sanctions.

President Barack Obama, whose legacy of foreign policy achievement rests squarely on the deal, made his strongest case for its passage last week, calling opponents no better than the Iranian mullahs.

"It's those hardliners chanting 'death to America' who have been most opposed to the deal. They're making common cause with the Republican caucus," Obama said.

He added, "If Congress kills this deal, we will lose more than just constraints on Iran's nuclear program or the sanctions we have painstakingly built," Obama said. "We will have lost something more precious: America's credibility as a leader of diplomacy. America's credibility as the anchor of the international system."

This newspaper agrees and urges Congress to abandon its hardline, largely partisan opposition.

Israel also must soften its position.

Just as President Obama was urging passage of the deal, Israeli Prime Minister Benjamin Netanyahu was speaking out against it.

"The nuclear deal with Iran doesn't block Iran's path to the bomb, it actually paves Iran's path to the bomb," he said.

Like the United States Israel has legitimate concerns about Iran's history of supporting terror, but we maintain the accord will achieve the principal goal of keeping it from developing nuclear weapons.

There must never be another Nagasaki or Hiroshima.