Elizabeth McIntosh,: Journalist who became an agent for the Office of Strategic Services whose efforts were crucial in the war in the East

Elizabeth McIntosh, who has died at the age of 100, conjured lies in the line of duty for the US Office of Strategic Services and as an author wrote about the women who used their brains, and sometimes their bodies, to help the spy agency in the Second World War.

The daughter of a sportswriter, McIntosh grew up in Hawaii and followed her father into journalism. She reported on women's issues for the Scripps Howard news service but grew restless after having witnessed the Japanese attack on Pearl Harbour in 1941. A family acquaintance with connections to the OSS, which later became the CIA, asked her, she recalled, "'Wouldn't you like to get into something interesting like...' You know, he didn't say 'spying', but he just said, 'more interesting maybe than the work you're doing.'"

She joined in 1943 and completed field-agent training in interrogation techniques, clandestine meetings and use of firearms. But cloak-and-dagger espionage or Mata Hari-style intrigue would not be her legacy. Instead, her fluency in Japanese and background as a reporter made her ideal for "morale operations", also known as "black" propaganda.

Stationed in New Delhi and later Kunming, China, where she befriended the future chef Julia Child, she participated in efforts to forge fake letters, documents, pamphlets and newspaper stories with realistic-seeming tales of suffering on the Japanese mainland. Such accounts – of starving youths and young women so traumatised by bombing that they were unable to bear children – reached Japanese troops by radio, airdrop, mail and other forms of subterfuge.

Japanese soldiers were known to be honour-bound to fight to the death, and McIntosh played a role in falsifying instructions designed to induce them to surrender more quickly in Burma towards the end of that campaign. The forgery vastly reduced Allied casualties.

On another occasion, McIntosh delivered an explosive masquerading as a lump of coal – the device was dubbed "black Joe" – to a Chinese operative of the OSS. The agent took the dynamite aboard a train ferrying Japanese soldiers and waited for the opportune moment to toss it into the engine before jumping to safety. The train blew up as it crossed a bridge.

Recounting the story in 2011, she confessed to some initial guilt over the many deaths. But she quickly reconsidered, saying about the TNT, "I was just the one who handed it to the guy who did the job."

One of her final operations involved funnelling misinformation to a Chinese fortune-teller whose radio show was a favourite of Japanese soldiers. She and a colleague drummed up various scenarios: an earthquake in Japan? Too commonplace. Maybe an earthquake and a tidal wave? They settled on something vague but catastrophic – "something we can't even mention because it is so dreadful and it is going to eradicate one whole area of Japan." That same day, the US dropped the atomic bomb on Hiroshima, prompting a colleague to ask how she knew about the top-secret programme.

After the war and in need of a job, McIntosh had a brief, miserable stint covering fashion for Glamour magazine before moving on to writing jobs for the Voice of America and the US State Department. From 1958-73 she worked for the CIA on classified operations that often used her burgeoning literary career as a cover.

Under her then-married name of Elizabeth MacDonald she had written a well-received memoir, Undercover Girl (1947), which featured an introduction by OSS founder William "Wild Bill" Donovan. In the foreword, he called her "a very effective agent."As Elizabeth Heppner, a later married name, she wrote two children's books in the late 1950s.

Her best-known book remains Sisterhood of Spies: The Women of the OSS (1998), which sketched the careers of many of the roughly 4,000 women who served the agency. Some were code clerks, analysts or secretaries in Washington. Others volunteered for riskier assignments. Virginia Hall, a well-born, multilingual Marylander who became known to the Nazis as the Limping Lady because of her artificial leg, helped Resistance fighter.

McIntosh lectured on the role of OSS women and became involved in a group called the OSS Society. "Betty McIntosh," said Charles Pinck, president of the Society, "represented the important and unheralded role that women have played in the US intelligence community since its inception."

Elizabeth Peet was born in Washington, where her father was sports editor for the Washington Herald. After high school in Hawaii, she graduated in 1935 from the University of Washington.

Her first marriage, to Alexander MacDonald, a journalist who served in the OSS in Thailand and later started the English-language Bangkok Post newspaper, ended in divorce. After the war she married Richard Heppner, who became deputy assistant secretary of defence for international security; he died in 1958. Her third husband, Frederick McIntosh, a former Air Force lieutenant colonel, died in 2004 after 42 years of marriage.

As a young reporter, McIntosh covered the Pearl Harbour raid and its aftermath, but she said her editors at the Honolulu Star-Bulletin would not run her story because it was too graphic in its description of blood-soaked children and other victims.

At her office, she wrote, "there were frantic calls from all sorts of women – housewives, stenographers, debutantes – wanting to know what they could do during the day, when husbands and brothers were away and there was nothing left but to listen to the radio and imagine that all hell had broken out on another part of the island.

"It was then that I realised how important women can be in a war-torn world."

Elizabeth Sebree Peet, Office of Strategic Services agent: born Washington 1 March 1915; married firstly Alexander MacDonald (marriage dissolved), secondly Richard Heppner (died 1958), thirdly Frederick McIntosh (died 2004); died Lake Ridge, Virginia 8 June 2015.

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