September 11, 2015 6:44 PM EDT

One night in early September, TIME went on a night patrol aboard the Commander Kazakos, a Greek coast-guard vessel. Over the past year, the 10-man crew of the Commander Kazakos has patrolled the front lines of the largest mass migration into Europe since World War II.

“One night I looked at the radar and saw eight of their boats coming toward us in a line,” recalls Border Guard Dmitrious Argyropoulos. “I thought to myself, ‘This can’t be happening.’”

More than a quarter-million migrants have reached the Greek islands by boat so far this year on their way to claim asylum in Western Europe, and nearly 3,000 have died in the attempt, according to the Greek government.

Click here for more coverage of the refugee crisis in Europe.

Write to Diane Tsai at diane.tsai@time.com.

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