It took three days for Carolyn Davidson Hill to get a chance to record what she had seen on the night of May 25, 1949, and in the wee hours of the next morning. “Now, at last, I get down to writing up that last, incredible 14 hours,” she told her diary then, recalling the decisive final battle between the Nationalist and Communist armies in their two-decade-old civil war for control of China.

Seventy years ago, Shanghai was, as it is today, China’s largest and most dynamic city, the economic engine driving much of the country’s growth and global power. It was also at the center of a war. As the People’s Liberation Army of the Chinese Communist Party advanced, the Nationalists, or Kuomintang party government, vowed to hold onto Shanghai at all costs.

With a brutal battle in the offing, most Westerners who lived there at the time packed up their things and left. Yet Hill and her husband Horace — or Hod, as she called him — hung on. The two, both 37, had married just six months earlier. Around that time, Hod took over as superintendent of Caltex, one of the largest oil terminals in China and a subsidiary of Texaco (today part of Chevron). Carolyn and Hod moved into a large, brick English-style house on the Caltex campus, about 15 miles by boat from central Shanghai, overlooked by Caltex’s hulking oil tanks, stacked barrels of airplane fuel and gasoline, and grimy brick factories and warehouses.

To protect the city’s river approaches, as Communist forces moved to encircle Shanghai in April of 1949, Kuomintang forces set up their regional battlefield headquarters next door to Caltex at China Petroleum Company’s terminal, putting the Hills squarely at the front lines.