A Boston man who lost most of his penis in a fight with cancer has become the first US patient to receive a penis transplant.

Thomas Manning, 64, a bank courier from Halifax, Massachusetts, received the new organ from a deceased donor in a 15 hour-long operation conducted at Massachusetts General Hospital in Boston on May 8 and 9. The procedure involves doctors hooking up nerves, veins, and arteries between the recipient and donor organ. So far, Manning's doctors are “cautiously optimistic” that he will recover urinary and sexual function in the coming weeks and months.

“It’s uncharted waters for us,” Dr. Curtis L. Cetrulo, a plastic and reconstructive surgeon, told the New York Times. Cetrulo was a leader on the team of seven surgeons, 6 fellows, and more than 30 other health care workers who contributed to Manning’s procedure.

Manning’s experimental procedure is the start of a program aimed at performing penis transplants for wounded veterans. As Ars reported last December, a group of doctors at Johns Hopkins University in Baltimore spearheaded the initiative, inspired by the 1,367 men—all aged under 35—that returned home from Iraq and Afghanistan between 2001 and 2013 with devastating genital injuries. “They’re 18- to 20-year-old guys, and they feel they have no hope of intimacy or a sexual life,” Cetrulo said. “They can’t even go to the bathroom standing up.” These men are at particularly high risk of suicide, Cetrulo noted.

But for early trials, the doctors will focus on civilians and training military medical staff because, as Cetrulo told the Times, the Department of Defense does not want veterans to act as “guinea pigs” after returning from war.

Manning’s transplant is only the third such procedure in the world—there have been a failed 2006 procedure in China and a successful 2004 procedure in South Africa, after which the recipient fathered a child.

Manning became a candidate for the transplant after a 2012 accident at work brought him to the hospital where doctors first noticed a cancerous growth on his penis. The rare cancer—which only affects around 2,000 men each year in the US—led to a partial penectomy. Manning was left with a one-inch stump and was unable to have sex or pee standing up.

He quickly volunteered for a transplant and was selected after a donor of Manning’s blood type and skin tone arrived in the New England Organ Bank. Jill Stinebring, the organ bank’s regional director, told the Times that requests for such donations were separate from those that apply to kidneys and other internal organs. Still, several families have consented to penis donations and none had refused, she said.

The doctors are planning more procedures, which are estimated to cost $50,000 to $75,000. For now, the hospitals involved are covering costs and doctors are donating their time. The next patient in line had his penis destroyed in a fire during a car crash. So far, the doctors are limiting the procedure to cancer and trauma patients and not considering gender reassignment surgeries.