When the US entered the war in April 1917, he joined the United States Army in May and was trained at Plattsburgh, New York and was commissioned as a second lieutenant in the Artillery on August 15, 1917.

In 1934, McCloy found new evidence allowing him to re-open an action for damages against Germany for the destruction caused by the 1916 Black Tom explosion.

His involvement in litigation over a World War I sabotage case gave him a strong interest in intelligence issues and in German affairs.

[13] Once the war started, McCloy was a crucial voice in setting US military priorities and played a key role in several notable decisions.

A key document was a Magic-decrypted interception of a Japanese diplomat in Los Angeles, who reported, "We also have connections with our second generations working in airplane plants for intelligence purposes.

[21] That led directly to the final resolution, in 1987, of the internment cases before the Ninth Circuit Court of Appeals, which fully exonerated Hirabayashi and other Japanese-American citizens, who fought the wartime curfews and forced relocations resulting from Army orders which the three-judge panel unanimously held were "based upon racism rather than military necessity.

"[22] The War Department was petitioned throughout late 1944 to help save Nazi-held prisoners by ordering the bombing of the railroad lines leading to Auschwitz and the gas chambers in the camp.

It could be executed only by the diversion of considerable air support essential to the success of our forces now engaged in decisive operations and would in any case be of such doubtful efficacy that it would not amount to a practical project."

"In fact, long range American bombers stationed in Italy had flown over Auschwitz several times that spring in search of the I.G.

"[23] In another series of letters, A. Leon Kubowitzki of the World Jewish Congress requested on 9 August 1944 that McCloy consider a message sent to them by Ernest Frischer of the Czechoslovak State Council from the War Refugee Board.

On the 14 August 1944 McCloy responded to Kubowitzki with a letter detailing how the operation would "be of such doubtful efficacy that it would not warrant the use of our resources," adding that "even if practicable, might provoke even more vindictive action by the Germans.

Battalion commander Frank Burke, a future Medal of Honor winner, ordered six soldiers of the 12th Infantry Regiment, 4th Division to march into Rothenburg on a three-hour mission and negotiate the surrender of the town.

American troops of the 12th Infantry Regiment, 4th Division occupied the town on April 17, 1945, and in November 1948, McCloy was named an honorary citizen (German: Ehrenbürger) of Rothenburg.

By mid-1945, the Japanese emperor began looking for ways to unwind the war, going as far as asking the Soviet Union to broker a peace between the United States and Japan.

[27] He argued that by doing so, it would enable the United States to claim a moral high ground, in the event that a bombing would be needed to thwart a Japanese mainland invasion.

[citation needed] While traveling by boat to the Potsdam Conference, Secretary of State James Byrnes convinced Truman to ignore McCloy's advice.

On March 17, 1949, McCloy and General Alvan Cullom Gillem, Jr. testified before the President's Committee on Equality of Treatment and Opportunity in the Armed Services.

McCloy was brought in to resolve the situation and was determined to make the bank an entity that would fund economically efficient projects, not just consumption.

At the strong urging of the West German government, and under massive pressure from the West German public, McCloy approved recommendations (including from the Peck Panel) for commuting of sentences of Nazi criminals including those of the prominent industrialist Alfried Krupp and Einsatzgruppe commander Martin Sandberger.

[30][31] Nuremberg judge William J. Wilkins wrote, Imagine my surprise one day in February 1951 to read in the newspaper that John J. McCloy, the high commissioner to Germany, had restored all the Krupp properties that had been ordered confiscated.

Two other death sentences from the Dachau trials were upheld by General Thomas T. Handy, that of Georg Schallermair and Hans-Theodor Schmidt.

Many were outraged that full amnesty had not been granted to the condemned, and it reached the point that McCloy's family started receiving death threats.

[33]McCloy supported the initiative of Inge Aicher-Scholl (the sister of Sophie Scholl), Otl Aicher and Max Bill to found the Ulm School of Design.

Following the 1953 death of Chief Justice Fred M. Vinson, President Eisenhower considered appointing McCloy in his place, but he was viewed as too favourable to big business.

[37] From 1954 to 1970, he was chairman of the prestigious Council on Foreign Relations in New York, to be succeeded by David Rockefeller, who had worked closely with him at the Chase Bank.

He later served as adviser to John F. Kennedy, Lyndon Johnson, Richard Nixon, Jimmy Carter and Ronald Reagan, and was the primary negotiator on the Presidential Disarmament Committee.

Notably, he was initially skeptical of the lone gunman theory, but a trip to Dallas with CIA veteran Allen Dulles, an old friend also serving on the commission, convinced him of the case against Lee Harvey Oswald.

In that capacity, he acted for the "Seven Sisters", the leading multinational oil companies, including Exxon, in their initial confrontations with the nationalization movement in Libya as well as negotiations with Saudi Arabia and OPEC.

In recognition of his efforts to the United States, he was presented with the Presidential Medal of Freedom with Distinction by President Lyndon B. Johnson on December 6, 1963.

His dedication contributed to a great extent to understanding of Berlin in the United States of America and to preservation of peace and freedom.